Current issue: Volume 53, Issue 8-9-10 2009-11-01 http://www.intjdevbiol.com http://www.intjdevbiol.com/web/covers/538-9-10o.jpg http://www.intjdevbiol.com 2009-11-01

If we identify Science and Scientific Research with what has been called Modern Western European Science, it is evident that the Kingdoms of the Iberian Peninsula were not involved significantly in its inception and spread (Basalla, 1967). This might appear to be paradoxical, since the huge Hispanic Empire (which included Portugal and its ultramarine possessions from 1580 to 1668), although already declining during the second half of the XVII Century, was still at the time the major power in the world. But, there were several reasons for this decline, many of them being causes which had been operating for centuries before they became visible...

Juan Aréchaga http://www.intjdevbiol.com 2009-11-01

We present a survey of the introduction and evolution of microscopy techniques in Spain, and the concepts and lines of research developed around this instrument, particularly in the field of Biomedical research. We cover in our article the long period from the XVII Century to the arrival of the great figure of Santiago Ramón y Cajal (1853-1934). We particularly want to mention many of the previously neglected pioneers who certainly paved the route for his discoveries and, we believe that without them, he would never have arrived to his important position in the annals of Biology and Medicine. The historical, scientific and social framework of that period also helped the approach to important biological concepts such as the cell and tissue, which are previous and essential ideas for a correct understanding of Development.

Roberto Marco-CuellarJuan Aréchaga http://www.intjdevbiol.com 2009-11-01

The contributions of Cajal to Neuroembryology are glossed with the help of a selection of images extracted from Cajal’s (1929) own synthesis of his neuroembryological output, laying emphasis on the persisting relevance and unsurpassed quality of many individual achievements and milestones he delivered on neurohistogenesis, practically throughout his career. Cajal’s theoretical background as regards embryology, morphology, comparative neuroanatomy and evolution is sketched at the beginning. The body of the review is divided into sections covering spinal cord, cerebellum, cortex, retina, sensory organs and muscular terminals, and astroglia. The deep and common-sensical conceptual analysis of neural histological variation during development performed by Cajal is highlighted at several points, as well as the places where he advanced genial conjectures that reached far forward in time, placing him still at the front of present day neuroembryological thinking. Some errors committed by Cajal are also commented upon. At one point (the retina), some of the present author’s own observations with a Golgi method variant are presented, as they complement observations that Cajal left incomplete because of technical problems. The major neuroembryological works of Cajal’s pupil Jorge F.Tello are mentioned at the end.

Luis Puelles http://www.intjdevbiol.com 2009-11-01

At the dawn of the 20th century in Lisbon, Augusto Celestino da Costa advocated a model of university practice based on research and defended the promotion of a scientific culture and the dissemination of Science in society. As a scientist, Celestino da Costa made numerous original descriptions of the cytology, histology and embryology of endocrine glands and the sympathetic nervous system. Celestino da Costa authored seminal textbooks on histology and embryology, and was responsible for launching in Portugal the first governmental agency to finance scientific activities.

José-Francisco David-Ferreira http://www.intjdevbiol.com 2009-11-01

Francisco Ort-Llorca (1905-1993) was one of the most outstanding Spanish embryologists of the XX century. He was disciple of Henri Rouvière in Paris (France), Alfred Fischel in Vienna (Austria), Walther Vogt in Munich (Germany) and Pedro Ara in Madrid (Spain). From 1935, he was professor of Human Anatomy at the Faculty of Medicine of Cadiz, belonged then to the University of Seville (accidentally, in the University of Valencia, during the Spanish Civil War from 1936-1939) and, later on, at the Faculty of Medicine of Madrid (Complutense University) from 1954 to 1975. He was internationally recognized in anatomical sciences and stood out for his contributions to descriptive and experimental Embryology and Teratology, particularly in those aspects connected to the normal and pathological development of the heart and visual organs.

Juan AréchagaJuan Jiménez-ColladoDomingo Ruano-Gil http://www.intjdevbiol.com 2009-11-01

At the beginning of the XXI Century, Spanish Biology lives a period of unprecedented growth and development. This situation owes much to the stability of the last few years and breaks a pattern in which Science was the activity of a few self-taught individuals working within an indifferent environment. The development of Genetics is a good example of these factors. A long isolated period dating back to the 1500s was broken at the beginning of the XX Century through the creation of a number of institutions and, in particular the Junta de Ampliacion de Estudios, which created a seed for scientific development and had a significant effect in the area of Genetics. However, the Spanish civil war destroyed this seed and forced a new beginning. Throughout the second half of the century, steady progress, largely driven by individuals formed abroad and returning to Spain with knowledge and methods, has been the basis for the establishment of a scientific ingrastructure from which Spain is making important contributions to modern biology. The person of Antonio Garcia-Bellido has emerged over the last 40 years as a reference for modern genetics and also as the root of an important, perhaps the only, real school in this area of work.

Alfonso Martinez-Arias http://www.intjdevbiol.com 2009-11-01

José Antonio Campos-Ortega (1940-2004), a Spanish scientist who became a leading figure in the developmental genetics of the nervous system, spent most of his scientific life in Germany. Nevertheless, he remained deeply rooted in his native country. His thinking, his ambition and his work were driven by scientific, philosophical and historical questions. He started as a neuroanatomist, working first in Valencia, then in Göttingen, Tübingen and Freiburg. He used primates, reptiles, then the house fly and finally Drosophila to address the question “How is the brain or the eye structured in order to function?”. While in Freiburg, the problem shifted to “How does the nervous system come into being, into form?” Campos-Ortega tried to understand early neurogenesis in Drosophila through formal genetics, by identifying relevant genes and studying their genetic interactions. Since he was convinced that not only a single experimental approach could solve a problem as complex as the development of the nervous system, he also included the molecular biological approach when he moved to Cologne, while maintaining a strong focus on anatomy, embryology and genetics. There, he also started to work on the neurogenesis of the zebrafish, using similar concepts and approaches. Throughout his scientific career, he thought, wrote and taught about the evolution of methods and ideas in his field of research. At Campos-Ortega’s early death, an unfinished book manuscript was left, entitled “Developmental Genetics. The Path to the Biological Synthesis”. Some parts of his introductory overview are included here.

Elisabeth KnustRainer Hertel http://www.intjdevbiol.com 2009-11-01

A history of Evolutionary Developmental Biology (Evo-Devo in short) in Spain is presented. From an almost total lack of research and tradition in Embryology, Genetics and Evolution throughout the 19th and well into the 20th century, evolution and development was first bridged in the 1970-80s by the structuralist approach of Pere Alberch and by important side-studies from the Madrid School of Developmental Genetics. A second stage was set in the early 1990s when a few scattered labs start to address problems which arose abroad by major advances in molecular phylogenetics and comparative gene expression patterns in selected animal models. The principal contributions included the nature and molecular features of the first bilaterians and the first chordates, the patterning of the vertebrate brain and limbs, and insect appendages and, on a finer scale, the roles of specific gene and gene families in vertebrate neural crest origin and in the patterning of sensory elements in the Drosophila species. Because a common genetic toolkit exists from sponges to man, current Evo-Devo research is taking a dual approach. On a "macroevolutionary" scale, it asks how and when developmental genes were assembled, at key points in the phylogenetic scale, into interacting functional networks to determine regional and tissue specific identities. On a "microevolutionary" scale, it analyzes how changes in the regulatory and codifying regions of specific genes correlate with specific morphological changes and how they could spread in natural populations. Given the paucity of such studies in current Spanish labs, a call is made to foster them.

Jaume Baguñà http://www.intjdevbiol.com 2009-11-01

The origins of modern Plant Developmental Biology in Spain can be traced back to a handful of scientists settled in Madrid, Barcelona, Valencia and Sevilla, who devoted themselves to plant biochemistry, molecular biology and genetics, and also to Drosophila developmental biology, which influenced, often unintentionally, the pioneers of this field. To reach the present day situation, the experience acquired in centres abroad has also been important, especially in plant research institutes in the USA, Germany (Max-Planck Institute für Züchtungsforschung) and United Kingdom (John Innes Centre). The contributions of Spanish scientists to the advancement of Plant Developmental Biology appears to be imbalanced towards reproductive biology, although relevant publications have also been reported on embryogenesis and seed development, shoot branching, tuberization, vascular morphogenesis, leaf development, regulation of development by light, signal transduction and hormone action and the connection between growth and development. Plant Developmental Biology in Spain is going through a flourishing time, with its future being highly dependent on i) appropriate funding conditions to its young scientists, ii) the opening of new areas of research, iii) the incorporation of technological breakthroughs into laboratories and iv) the carrying out of cooperative research by means of networking. Currently, besides many Departments of the Spanish universities, several centres in which competitive research in plant Developmental Biology can be accomplished, exist: the CNB and CBGP in Madrid, the LGMV CSIC-IRTA in Barcelona, the IBMCP CSIC-UPV, in Valencia and the IBVF CSIC-USE in Sevilla. Let's go for more!

José-Pío Beltrán http://www.intjdevbiol.com 2009-11-01

Developmental Biology has established itself as a solid field of teaching and research in Portugal. Its history is recent, generally considered to have started with the pioneering work of Augusto Celestino da Costa at the beginning of the 20th century. However, research groups were very few and, until the early 1990’s, teaching beyond morphological and comparative embryology was uncommon. In 1994, the first university course dedicated to Developmental Biology as a separate field from Embryology was created at the Faculty of Sciences of the University of Lisbon and a course on Plant Differentiation and Morphogenesis was also initiated. A Masters programme in Developmental Biology followed at the Lusófona University in 1996. Subsequently, modules of Developmental Biology were included in many Embryology courses and eventually more Developmental Biology courses were created. From 1999 onwards, the number of research groups working in Developmental Biology started to increase, many of which were initiated by researchers who had had the opportunity to pursue their PhD and/or post-doc studies abroad. The Instituto Gulbenkian de Ciência (Gulbenkian Institute of Science) became the first home of most of these groups, but several later spread to other institutions. This increased activity in turn has stimulated teaching of Developmental Biology and more students have been getting interested in the field. This “positive feedback loop” makes it a nice time to be teaching and working in Developmental Biology in Portugal.

Sólveig ThorsteinsdóttirGabriela RodriguesEduardo G. Crespo http://www.intjdevbiol.com 2009-11-01

Developmental biology and/or embryology prospectuses in Spanish universities are reviewed. From old masterly classes to virtual teaching, a variety of methods are being used nowadays to teach these subjects. In a country like Spain, adapting to the European Higher Education Space, old and new teaching methods are educational alternatives in a university model which respects both tradition and modernity. In this report, consensus guidelines, concluded from this general survey, are suggested for teachers to ensure future progress.

Manuel Marí-Beffa http://www.intjdevbiol.com 2009-11-01

Portugal celebrated in 2006 its first 20 years of the formal introduction of the practice of external evaluation of research proposals in the national funding system. Accounts of changes in numbers of publications, citations, numbers of research projects funded and budget figures can be found in Government Reports (www.oces.mctes.pt.). An offshoot of the decisive and firm implementation of that practice in what was to become the Health Sciences was that the area became an attractor for young researchers in the basic biological sciences, namely, molecular, cellular and developmental biology. Reciprocally, the entry of basic biological scientists into medically oriented groups totally changed the landscape, the soil, the seeding, the cross-fertilization and the flowering of biomedical research in the country. This paper is a personal account of the experience of a scientist who was asked by the then President of the National Research Council, José Mariano Gago to co-ordinate the introduction of external evaluation of research projects and research institutes in the Health Sciences in Portugal between 1986 and 1997.

Maria De Sousa http://www.intjdevbiol.com 2009-11-01

We revise the historical evolution of the societies devoted to Developmental Biology from the early activities of the Institut International d´Embryologie (IIE), founded in 1911, with particular emphasis on the more recent constitution of the Spanish Sociedad Española de Biología del Desarrollo (SEBD), founded in 1994, and the Portuguese Sociedade Portuguesa de Biologia do Desenvolvimento (SPBD), founded in 2006. We also describe the role played by The International Journal of Developmental Biology (IJDB) in the constitution of the SEBD and its projection and support to international Developmental Biology societies and individual researchers in the world, according to its mission to be a non-for-profit publication for scientists, by scientists.

Isabel PalmeirimJuan Aréchaga http://www.intjdevbiol.com 2009-11-01

Developmental Biology in Portugal and Spain has been running along mostly parallel tracks - until recently. It is the youngest generations who, driven by an increasing interest in the science and culture of each other’s country, are bringing the situation to its natural state: one of strong and fruitful collaboration between Iberian labs.

Fernando Casares http://www.intjdevbiol.com 2009-11-01

Jose Francisco David-Ferreira is one of the most influential Professors of Cell and Developmental Biology in Portugal. David-Ferreira pioneered the use of electron microscopy in cell biology and experimental embryology. He also paved the way for successive generations of biologists who cross-fertilized the national scientific community. As we discuss briefly below, David-Ferreira is above all a Pedagogue and an Institution builder.

Maria Carmo-Fonseca http://www.intjdevbiol.com 2009-11-01

This interview with Antonio García-Bellido explores three aspects of his work. First and foremost is the origin of his contributions: trying to define what allowed him to become a pioneer of developmental genetics. The second part deals with the nature of his major contributions, as seen by himself. In a third section he expresses his views on a number of subjects that relate mostly to the future of developmental biology and to evolution. A list of his most significant publications is appended as an annex.

Alain Ghysen http://www.intjdevbiol.com 2009-11-01

In this essay, we discuss the contribution of local cell interactions, as opposed to global cues, such as hormones and morphogens, to the determination of the size and shape of organs. This internalistic notion is based on the integration of physiological experiments, clonal analysis and genetic mosaics of morphogenetic mutants. Physiological experiments such as regeneration, cell dissociation and re-aggregation, and feeder layers, reveal the existence of regional specificities related to regional patterning, positional values and cell polarity. On the other hand, clonal analysis shows homogeneous and exponential growth by mitosis associated with oriented cell divisions along two axes of growth. Preferential mitotic orientations are also regional characteristic. Finally, genetic mosaics of morphogenetic mutants help to understand the genetic and eventually the molecular bases of morphogenesis, revealing the modes of cell behavior (such as positional accommodation, mitotic orientations, cell affinities and cell recognition) at work in the generation of the constant sizes and shapes of Drosophila imaginal structures. These classical and recent findings contribute to a more updated Entelechia model of morphogenesis.

Antonio García-Bellido http://www.intjdevbiol.com 2009-11-01

Data on the molecular and genetic basis of animal development, and on genome sequences, have been challenging our established assumptions about animal evolution for the last decade. Recent such data in animals of particular phylogenetic importance beg us to take another look at whether similarities in developmental and genetic mechanisms in current animals are the product of a common inheritance (homology) or convergent evolution (analogy). The evolution of segmentation, in particular whether segmentation and metameric bodies have arisen just once or several times in evolution, is a prime concern. Segmentation and metamerism are striking developmental and body organisations that exist, in varying degrees, in many complex animals, but the traditional view holds that this is the result of convergent evolution. Here, I review recent palenotological and developmental information and conclude that a metameric body plan is not only a likely ancestral character of bilaterian animals, but also a possible trigger for the Cambrian explosion in body morphology and complexity. This conclusion is supported by the phylogenetic distribution and prevalence of metameric phyla in the Cambrian, and the similarity of the genomes and segmentation mechanisms across current bilaterian phyla.

Juan Pablo Couso http://www.intjdevbiol.com 2009-11-01

Planarians can undergo dramatic changes in body size and regenerate their entire body plan from small pieces after cutting. This remarkable morphological plasticity has made them an excellent model in which to analyze phenomena such as morphogenesis, restoration of pattern and polarity, control of tissue proportions and tissue homeostasis. They have a unique population of pluripotent stem cells in the adult that can give rise to all differentiated cell types, including the germ cells. These cellular characteristics provide an excellent opportunity to study the mechanisms involved in the maintenance and differentiation of cell populations in intact and regenerating animals. Until recently, the planarian model system lacked opportunities for genetic analysis; however, this handicap was overcome in the last decade through the development of new molecular methods which have been successfully applied to planarians. These techniques have allowed analysis of the temporal and spatial expression of genes, as well as interference with gene function, generating the first phenotypes by loss or gain of function. Finally, the sequencing of the planarian genome has provided the essential tools for an in-depth analysis of the genomic regulation of this model system. In this review, we provide an overview of planarians as a model system for research into development and regeneration and describe new lines of investigation in this area.

Emili SalóJosep F. AbrilTeresa AdellFrancesc CebriáKay EckeltEnrique Fernández-TaboadaMette Handberg-ThorsagerMarta IglesiasM. Dolores MolinaGustavo Rodríguez-Esteban http://www.intjdevbiol.com 2009-11-01

Stem cells possess the unique properties of self-renewal and the ability to give rise to multiple types of differentiated tissue. The fruit fly Drosophila melanogaster retains several populations of stem cells during adulthood as well as transient populations of stem cells during development. Studies of these different populations of stem cells using the genetic tools available to Drosophila researchers have played an important role in understanding many conserved stem cell characteristics. This review aims highlight some of the recent contributions from this important model system to our understanding of the myriad of processes that interact to control stem cell biology.

John PearsonLourdes López-OnievaPatricia Rojas-RíosAcaimo González-Reyes http://www.intjdevbiol.com 2009-11-01

Apoptosis (programmed cell death) is a conserved process in all animals, used to eliminate damaged or unwanted cells after stress events or during normal development to sculpt larval or adult structures. In Drosophila, it is known that stress events such as irradiation or heat shock give rise to high apoptotic levels which remove more than 50% of cells in imaginal discs. However, the surviving cells are able to restore normal size and pattern, indicating that they undergo additional proliferation. This “compensatory proliferation” is still poorly understood. One widely used method to study the properties of apoptotic cells is to keep them alive by expressing in them the baculoviral protein P35, which blocks the activity of the effector caspases. These "undead" cells acquire special features, such as the emission of the growth signals Dpp and Wg, changes in cellular morphology and induction of proliferation in neighbouring cells. Here, we review the various methods used in Drosophila to block apoptosis and its consequences, and focus on the generation and properties of undead cells in the wing imaginal disc. We describe their effects in epithelial architecture and growth in some detail, and discuss the possible relationship between undead cells and compensatory proliferation.

Francisco A. MartínAinhoa Peréz-GarijoGinés Morata http://www.intjdevbiol.com 2009-11-01

The posterior spiracle has become one of the best systems to study how Hox genes control morphogenesis. Interaction of Abdominal-B (ABD-B) with dorso ventral and intrasegmental positional information leads to the local activation of ABD-B primary targets in the dorsal region of the eighth abdominal segment (A8). Primary targets pattern the spiracle subdividing it into two broad areas: external stigmatophore vs. internal spiracular chamber precursor cells. Primary targets then activate secondary targets and modulate the expression of signalling molecules in the spiracle primordium creating unique spiracle positional values. This genetic cascade activates the “realisator” genes that modulate the cell behaviours causing invagination, elongation and cell rearrangements responsible for spiracle morphogenesis. The spiracle realisators that have been identified to date correspond to cell adhesion proteins, cytoskeleton regulators and cell polarity molecules. Interestingly, these realisators localise to different apico-basal locations in the cell (RhoGEF apical, Crumbs subapical, E-cadherin in the adherens junction, RhoGAP basolateral). Therefore, the Hox anterior-posterior code is converted in the cell into apico-basal information required to implement the posterior spiracle morphogenetic program. We believe this may be a common characteristic for Hox induced organogenesis.

James Castelli Gair HombríaMaría Luisa RivasSol Sotillos http://www.intjdevbiol.com 2009-11-01

Pallid anchovy fillet, friendly filtering, peacefully laying and little lancelet are some of the nicknames and adjectives the cephalochordate amphioxus has received throughout the last two centuries. Traditionally regarded as the living representative of the last ancestor of vertebrates, amphioxus has recently been promoted to the privileged position of being the most ancient chordate. The preliminary analysis of its prototypical genome is nearly completed, and its hidden secrets towards the understanding of the primitive chordate and deuterostome genomes will soon see the light. Amphioxus embryonic development and body plan have remained in evolutionary stasis since the cephalochordate lineage split from the chordate ancestor about 500 million years ago. In contrast, amphioxus research is far from being at a standstill; in Europe, thanks to the international cooperation and the Banyuls Oceanographic Station, amphioxus embryos are obtained on demand during the spawning season. We summarise here our progress towards the dream of the experimental manipulation of the amphioxus embryo, to enter the era of Experimental Evo-Devo.

Senda Jimenez-DelgadoJordi Garcia-FernandezJuan Pascual-AnayaIgnacio MaesoManuel IrimiaCarolina MinguillonElia Benito-GutierrezJosep GardenyesStephanie BertrandSalvatore D'Aniello http://www.intjdevbiol.com 2009-11-01

The sequencing of the whole genome of multiple species provides us with the instruction book of how to build an organism and make it work, plus a detailed history of how diversity was generated during evolution. Unfortunately, we still understand only a small fraction, which is locating where genes are and deciphering the proteins they code for. The next step is to understand how the correct amount of gene products are produced in space and time to obtain a fully functioning organism, from the egg to the adult. This is what is known as the regulatory genome, a term coined by Eric H. Davidson. In this review, we examine what we know about gene regulation from a genomic point of view, revise the current in silico, in vitro and in vivo methodological approaches to study transcriptional regulation, and point to the power of phylogenetic footprinting as a guide to regulatory element discovery. The advantages and limitations of each approach are considered, with the emerging view that only large-scale studies and data-crunching will give us insight into the language of genomic regulatory systems, and allow the discovery of regulatory codes in the genome.

M. Eva AlonsoBárbara PernauteMiguel CrespoJoséluis Gómez-SkarmetaMiguel Manzanares http://www.intjdevbiol.com 2009-11-01

During Notch mediated lateral inhibition, interacting cells establish or amplify differences in Notch signalling, which are then translated into distinct cell fate decisions according to the developmental context. In recent years, several mechanisms that increase the signalling capacity of interacting cells have been uncovered (reviewed in Bray, 2006, Le Borgne, 2006, Schweisguth, 2004). However, mechanisms specifically targeted to downregulate receptor activity are also at work during lateral inhibition, contributing decisively to generate definitive differences between interacting cells. In this review, we discuss some of these mechanisms and their relevance for the overall architecture of the Notch pathway. We further highlight the importance of properly terminating Notch activity during cell fate decisions mediated by this pathway.

Rita FiorDomingos Henrique http://www.intjdevbiol.com 2009-11-01

The genes of the spalt (sal) family play fundamental roles during animal development. The two members of this family in Drosophila, spalt (sal) and spalt-related (salr) encode Zn-finger transcription factors that link the Decapentaplegic (Dpp)/BMP signalling pathway to the patterning of the wing. They are regulated by the Dpp pathway in the wing disc, and they were shown to mediate some of the morphogenetic activities of the Dpp/BMP4 secreted ligand. The sal genes were initially found by virtue of mutations that produce homeotic transformations in the head and tail of the Drosophila embryo. Since then, a number of other requirements have been associated to these genes in Drosophila, including morphogenesis of the respiratory system, cell fate specification of sensory organs and the differentiation of several photoreceptor cells, among others. Vertebrate sal orthologues (spalt-like/sall) have also important developmental roles during neural development and organogenesis, and at least two human sall genes are linked to the genetic diseases Townes Brocks Syndrome (TBS; SALL1 ) and Okihiro Syndrome (OS; SALL4 ). In this review, we will summarize the main characteristics of the sall genes and proteins, pointing out to the similarities in their developmental roles during Drosophila and vertebrate development.

Jose F. de CelisRosa Barrio http://www.intjdevbiol.com 2009-11-01

One fundamental aspect of vertebrate embryonic development is the formation of the body plan. For this process, asymmetries have to be generated during early stages of development along the three main body axes: Anterior-Posterior, Dorso-Ventral and Left-Right. We have been studying the role of a novel class of molecules, the Cerberus/Dan gene family. These are dedicated secreted antagonists of three major signaling pathways: Nodal, BMP and Wnt. Our studies contribute to the current view that the fine tuning of signaling is controlled by a set of inhibitory molecules rather than by activators. In this context, the Cerberus-like molecules emerge as key players in the regulation and generation of asymmetries in the early vertebrate embryo.

José A. BeloAna C. SilvaAna C. BorgesMário FilipeMargaret BentoLisa GonçalvesMarta VitorinoAna-marisa SalgueiroVera TexeiraAna T. TavaresSara Marques http://www.intjdevbiol.com 2009-11-01

The Hox genes specify different structures along the anteroposterior axis of bilaterians. They code for transcription factors including a conserved domain, the homeodomain, that binds DNA. The specificity of Hox function is determined by each gene controlling the expression of different groups of downstream genes. These can be other transcription factors, elements in signaling pathways or realizator genes that carry out basic cellular functions. In regulating specific targets, the Hox genes interact with members of signaling pathways and with other proteins, thus forming part of gene networks that contribute to the modification of homologous structures or to the creation of new organs.

David ForondaLuis F. de NavasDaniel L. GarauletErnesto Sánchez-Herrero http://www.intjdevbiol.com 2009-11-01

Embryonic development is strictly regulated both in time and in space. This extraordinary control is clearly evidenced during the process of somitogenesis. In this process, pairs of somites are formed periodically, such that the time required to form a new somite pair is constant and species specific. The tight temporal control underlying somitogenesis has been shown to depend upon a molecular clock, manifested by the cyclic expression of an increasing number of genes in the unsegmented paraxial mesoderm. Portuguese researchers have been intimately connected to the achievements that have been made in this new field of research: the somitogenesis molecular clock. This article intends to report the Portuguese contributions to the discovery and characterization of the molecular clock underlying somite formation and possibly other embryonic processes. This work inspired many scientists around the world and it has been followed in Portugal by teams that keep on pursuing the characterization of the machinery of this molecular oscillator and its function in the acquisition of both temporal and positional information during development.

Isabel PalmeirimSusana Pascoal http://www.intjdevbiol.com 2009-11-01

The vertebrate heart is unique among the blood pumps described in metazoans. In contrast to the myoepithelial tubes found in most animal phyla, the vertebrate heart is made up of multilayered myocardial cells surrounded by connective tissue derived from epicardium and endocardium, and endowed with complex valvular, coronary vessel and conduction systems. Despite these profound differences, a common genetic program seems to underlie the specification and differentiation of all the cardiac tissues. In this article, we will review the similarities in the transcriptional networks and signalling mechanisms regulating cardiac development in different animals, as well as the origin of the main differences existing between vertebrate and invertebrate hearts. We will pay special attention to the hypotheses concerning the evolutionary origin of the endothelium and the epicardium from ancestral blood cells and pronephric progenitors, respectively. We can summarize the transition between the invertebrate and the vertebrate heart as the result of the thickening of the primarily myoepithelial cardiac tube which was concomitant with: 1) an inner lining by an endothelium with the ability to transform into mesenchyme; 2) an outer lining derived from an ancestral pronephric glomerular primordium with vasculogenic potential; 3) a neural crest cell population which reaches the heart from the pharyngeal region; 4) the incorporation of new myocardium at both ends from a second heart field and 5) the formation of specialized chambers. The complex interactions between all these elements originated an exceptionally powerful blood pump which allowed vertebrates to reach their characteristically large size and activity.

José M. Pérez-PomaresJuan M. González-RosaRamón Muñoz-Chápuli http://www.intjdevbiol.com 2009-11-01

ate maps are required to address questions about the commitment and differentiation of precardiac cells. Here, we report a detailed study of the precardiac cells located at the level of the primitive streak, employing different experiments with a variety of techniques combining double transplantations, microinjections and immunocytochemistry. Most cells of the more rostral segments of the primitive streak were found to contribute cells to the endodermal layer, adjacent to precardiac mesodermal cells of the heart forming region whose provenance was in the immediately more caudal segments of the primitive streak. We established a close spatio-temporal relationship between the two cell layers and the expression of their specific cardiac markers (cNkx-2.5, Bmp2, Cripto, Usmaar, dHand, GATA4, Pitx2, Hex, Fgf8, AMHC1 and VMHC1). We also analyzed the ability of precardiac cells to differentiate when they are transplanted to ectopic locations or are subjected to the influence of the organizer. We propose that the precardiac cells of the primitive streak form at least two groups with different significance. One, regulated by mediation of the organizer, is located preferentially in the more rostral region of the primitive streak. It consists of the prospective cells of the endoderm layer, with a hierarchic pattern of expression of different genes characterized by its capacity for induction and regulation of a second group of cells. This second group is located preferentially in the more caudal segments, and is fated to form the precardiac mesoderm, whose differentiation would be characterized by the expression of various specific genes.

Carmen Lopez-SanchezNatividad Garcia-MasaCarlos M. GañanVirginio Garcia-Martinez http://www.intjdevbiol.com 2009-11-01

The aim of this study was to determine the effects of forced expression of myocd-A in the left ventricular (LV) myocardium on cardiac performance in early neonatal piglets. LV transfection with the gene for homeodomain only protein (hop), an antagonist of myocd-mediated activities, was also performed. Gene delivery was performed in 6-day-old piglets using a low-traumatic, catheter-based, video-assisted procedure developed by us for direct intra-myocardial injections of plasmid DNA into 3-4 target areas of the ventral LV free wall (LVFW). Two isoforms of porcine myocd were identified, cloned and characterized: the exon 11-lacking myocd-A and its larger exon 11-containig variant, myocd-B. In neonatal piglets, myocd-A seems to be a cardio-predominant isoform enriched in the LVFW/septum, whereas the myocd-B isoform is detected not only in the heart but also in various smooth muscle cell-containing tissues. Intramyocardial myocd-A gene delivery resulted in forced transgene expression in the target areas of the LVFW as compared to controls. On day 2 post-delivery, a marked decrease of LV-end systolic pressure values (an accepted marker for impaired LV function) was observed in myocd-A-transfected piglets as compared to hop-transfected and control groups. In addition, forced myocd-A expression in the LVFW caused abnormal ECG. A significant up-regulation of the gene for fetal-predominant muscle light chain 3F myosin was detected in myocd-A-transfected LVFWs harvested on day 2 post-delivery. Extended analysis on day 7 post-delivery revealed a drop decrease in myocd-A transgene expression in target LVFW regions which was correlated with normalization of the LV systolic parameters in experimented piglets.

Mario TorradoAlberto CentenoEduardo LópezAlexander T. Mikhailov http://www.intjdevbiol.com 2009-11-01

In vertebrates, the paraxial mesoderm differentiates into several structures, including the axial skeleton. The genetic mechanisms that control positional information in the paraxial mesoderm along the anterior-posterior axis are responsible for the development of a skeleton with the appropriate vertebral formula, i.e. a specific number of cervical, thoracic, lumbar, sacral and caudal vertebrae. These control mechanisms are complex and involve molecules of different kinds, including transcription factors, like those encoded by the Hox genes, and signalling molecules, like those involved in Gdf11, FGF, retinoic acid or WNT signalling. Recent experiments indicate that most of the positional information for the paraxial mesoderm is encoded during the initial steps of its development in the presomitic mesoderm, although it is only decoded later during differentiation of the somites. The genesis of positional identity may be linked to the process of somitogenesis, which also occurs in the presomitic mesoderm as a result of complex interactions involving oscillatory activity of components of the Notch and WNT signalling pathways and antagonistic gradients of FGF/WNT and retinoic acid. The possible connections between Hox genes and all these signalling processes to generate a properly patterned axial skeleton are discussed in this review.

Moisés MalloTânia VinagreMarta Carapuço http://www.intjdevbiol.com 2009-11-01

During limb development, expression of the TALE homeobox transcription factor Meis1 is activated by retinoic acid in the proximal-most limb bud regions, which give rise to the upper forelimb and hindlimb. Early subdivision of the limb bud into proximal Meis-positive and distal Meis-negative domains is necessary for correct proximo-distal (P-D) limb development in the chick, since ectopic Meis1 overexpression abolishes distal limb structures, produces a proximal shift of limb identities along the P-D axis, and proximalizes distal limb cell affinity properties. To determine whether Meis activity is also required for P-D limb specification in mammals, we generated transgenic mice ectopically expressing Meis1 in the distal limb mesenchyme under the control of the Msx2 promoter. Msx2:Meis1 transgenic mice display altered P-D patterning and shifted P-D Hox gene expression domains, similar to those previously described for the chicken. Meis proteins function in cooperation with PBX factors, another TALE homeodomain subfamily. Meis-Pbx interaction is required for nuclear localization of both proteins in cell culture, and is important for their DNA-binding and transactivation efficiency. During limb development, Pbx1 nuclear expression correlates with the Meis expression domain, and Pbx1 has been proposed as the main Meis partner in this context; however, we found that Pbx1 deficiency did not modify the limb phenotype of Msx2:Meis1 mice. Our results indicate a conserved role of Meis activity in P-D specification of the tetrapod limb and suggest that Pbx function in this context is either not required or is provided by partners other than Pbx1.

Nadia MercaderLicia SelleriLuis Miguel CriadoPilar PallaresCarlos ParrasMichael L. ClearyMiguel Torres http://www.intjdevbiol.com 2009-11-01

Here we report the pattern of expression of inhibitor of DNA binding/differentiation factor 2 (Id2) in the developing chicken limb. We show that prior to stage 25, Id2 is expressed in the anterior and posterior mesoderm, the AER, and in the early skeletal chondrogenic aggregates. At more advanced stages of limb development Id2 is expressed in the undifferentiated subectodermal and interdigital mesenchyme and exhibits specific domains of expression in the growing digits. These expression domains were closely coincident with zones of activation of BMP-signaling as deduced from the distribution of phosphorylated SMADs 1/5/8. In micromass cultures transcripts of Id2 are associated with the nodules of chondrogenic differentiation. Expression of Id2 both in vivo and in vitro was up-regulated in experiments of BMP-gain-of-function and down-regulated after treatments with BMP-antagonists. Interestingly, interdigital application of TGFbeta2 transiently upregulates Id2 in coincidence with the inhibition of interdigital cell death and the commitment of the interdigital mesenchyme to form an ectopic digit. These data suggest that Id2 is a molecular mediator of BMP signaling acting in concert with the TGFbeta pathway during the formation of the digits.

Carlos I. Lorda-DiezNuria Torre-PérezJuan A. García-PorreroJuan M. HurleJuan A. Montero http://www.intjdevbiol.com 2009-11-01

The inner ear is a complex structure responsible for the senses of audition and balance in vertebrates. The ear is organised into different sense organs that are specialised to detect specific stimuli such as sound and linear or angular accelerations. The elementary sensory unit of the ear consists of hair cells, supporting cells, neurons and Schwann cells. Hair cells are the mechano-electrical transducing elements, and otic neurons convey information coded in electrical impulses to the brain. With the exception of the Schwann cells, all cellular elements of the inner ear derive from the otic placode. This is an ectodermal thickening that is specified in the head ectoderm adjacent to the caudal hindbrain. The complex organisation of the ear requires precise coupling of regional specification and cell fate decisions during development, i.e. specificity in defining particular spatial domains containing particular cell types. Those decisions are taken early in development and are the subject of this article. We review here recent work on: i) early patterning of the otic placode, ii) the role of neural tube signals in the patterning of the otic vesicle, and iii) the genes underlying cell fate determination of neurons and sensory hair cells.

Berta AlsinaFernando GiraldezCristina Pujades http://www.intjdevbiol.com 2009-11-01

Programmed cell death is a well established key process required for proper development of the nervous system. The regulatory and executor mechanisms controlling survival/death of projection neurons, as well as of other types of differentiated neurons and glial cells, have been studied intensely during neural development. Much less attention has been paid to earlier cell death events affecting neuroepithelial cells and recently born neurons and glial cells. We review here the reports on cell death during vertebrate retina development, our model system for many years, which has provided clear evidence of the importance of early neural cell death. We tentatively categorize the available observations in three death phases, namely morphogenetic cell death, early neural cell death and neurotrophic cell death. The magnitude and the precise regulation of the early phases of cell death are fully comparable to the much better characterized neurotrophic cell death. Therefore, early neural cell death deserves a profound dedicated study; this will help to obtain an integrated understanding of the development of the retina and other parts of the vertebrate nervous system.

Ana I. ValencianoPatricia BoyaEnrique J de la Rosa http://www.intjdevbiol.com 2009-11-01

Pluripotent cells can be isolated from the mammalian inner cell mass (ICM) of the embryo at the blastocyst stage, and maintained in culture as undifferentiated, embryonic stem cells (ES). These cells are an important model of mammalian development in vitro and are the focus of a great deal of research for their use in Cell Therapy. In vivo, shortly after the blastocyst stage, the ICM segregates into two layers: the hypoblast which will give rise to the yolk sac, and the epiblast. Epiblast stem cells, like ES cells, are pluripotent. The epiblast will differentiate very early into germ cell progenitors, the primordial germ cells (PGC). PGCs can give rise to embryonal carcinoma cells, the pluripotent stem cells of testicular tumors. During normal embryo development, PGCs migrate into the aorta-gonad-mesonephros region (AGM). Interestingly, this region also harbors the first wave of embryonic hematopoiesis. Subsequent waves of hematopoiesis involve AGM-hematopoietic stem cell (HSC) colonization of the fetal liver, thymus, spleen and ultimately, for adult hematopoiesis, the bone marrow (BM). The BM is also source of mesenchymal stem cells (MSCs). It is accepted that the AGM region cells give rise to the mesothelial cells which are the embryonic precursors of the HSC and MSC of the BM. Recent identification of a subpopulation of cells with markers typical of PGCs in the adult BM, which are capable of differentiating into HSCs, suggests that HSCs originate from a common precursor of PGCs and HSCs derived from the epiblast. Several groups have described the presence of stem cells with the same markers in epidermis, bronchial epithelium, pancreas, retina, hair follicle, heart and dental pulp among, other organs. This presence supports the hypothesis that during early development, epiblast/germ line-derived cells are deposited in various organs which persist into adulthood. The question remains whether these pluripotent stem cells are only developmental remnants or if they continuously contribute to the renewal of tissues, and thus can be reactivated for tissue regeneration without the need for stem cell transplantation for human cell therapies.

Maria P. De MiguelFrancisco Arnalich MontielPilar Lopez IglesiasAlejandro Blazquez MartinezManuel Nistal http://www.intjdevbiol.com 2009-11-01

The epithelial to mesenchymal transition (EMT) is a fascinating phenotypic change that is undertaken by embryonic and adult cells in physiological and pathological conditions, respectively. This change in cell behavior involves the loss of epithelial characteristics and the acquisition of migratory properties. While it has long been established as a fundamental process in the generation of many different embryonic tissues, its significance during tumor progression as an initial determining step in the metastatic cascade has remained a matter of debate. Recent molecular analyses coupled with state-of-the-art imaging technology have helped to define the EMT as an important landmark, not only during tumor progression, but also during the development of other pathologies such as organ fibrosis. Spanish groups have contributed to the analysis of EMT both from the developmental and the pathological point of view, in particular assessing the implication of the Snail genes in this process. Interestingly, the contribution of Spanish scientists to the existence of EMT in tumors possibly goes back more than 100 years, when Cajal referred to some “pear-like cells, not attached to each other” in his description of human breast carcinomas.

M. Angela Nieto http://www.intjdevbiol.com 2009-11-01

Epithelia have the essential role of acting as a barrier which protects living organisms and its organs from the surrounding milieu. Therefore, it is crucial for epithelial tissues to have robust ways of maintaining its integrity despite the frequent damage caused by injury, inflammation and normal cell turnover. All epithelia have some capacity to repair themselves. However, the wound-healing process differs dramatically between the developmental stage and the type of tissue involved. In this review, we will not analyse all aspects of wound healing; instead we will focus on the capacity which several simple epithelial tissues have to reseal small discontinuities very rapidly and efficiently, a process that we call epithelial resealing. We will start by describing the initial experiments which demonstrated the existence of a purse string mechanism to repair embryonic wounds and we will compare this mechanism with embryonic morphogenetic movements which resolve epithelial discontinuities that arise during the normal course of development. We will then discuss other contexts in which epithelia resealing occurs, both in cell culture systems and in adult tissues, and which suggest that at least some of the mechanisms that regulate epithelial resealing may be conserved, acting in several types of simple epithelia, both in embryos and in adults, and across species.

Beatriz Garcia-FernandezIsabel CamposJennifer GeigerAna C. SantosAntonio Jacinto http://www.intjdevbiol.com 2009-11-01

Mutations in the CDH1 gene, which encodes the cell adhesion molecule E-cadherin, are associated with hereditary diffuse gastric cancer in humans. Although most of the CDH1 mutations found are truncating, leading to non-functional E-cadherin, some are missense. These missense E-cadherin mutants result in full-length proteins which, when assayed in cell culture, still retain some biological activity. In order to understand the molecular causes of the malfunction of the E-cadherin missense forms found in patients, we developed a Drosophila model, where the effects of expressing the mutant forms can be studied in vivo (Pereira et al., 2006). Here, we review the results obtained so far, and outline possible ways of exploiting the fly model system to screen for pathways affected by specific E-cadherin missense mutant forms and to identify mechanisms that contribute to tumourigenesis.

Joana CaldeiraPaulo S. PereiraGianpaolo SurianoFernando Casares http://www.intjdevbiol.com 2009-11-01

In recent years, the reversion of the cancer phenotype of human melanoma cells in developing zebrafish and chick embryos has been reported. The aim of this review is to revise these and other related contributions regarding the regulation of embryonic cancer and to provide a framework with which to understand results from our laboratory on the interactions of human melanoma cells with post-implanted mouse embryos cultured in vitro. To this end, we used the A375 human melanoma cell line transfected with the green fluorescent protein (GFP) gene. Labeled cells were transplanted onto the surface of the developing visceral endoderm of 7.5 dpc mouse embryos. Subsequently, we cultured the transplanted embryos for three days and monitored the movements of GFP labeled human melanoma cells by confocal microscopy. Our results show that ectopic melanoma cells internalize and migrate inside the embryo body in a way reminiscent of neural crest cells. The absence of localized tumor growth after 72 hours of in vitro embryo co-culture suggests that malignant phenotype inhibiting factors are active at the gastrulating stage and during early organogenesis. These results complement previous reports of growth regulation of B16 mouse melanoma cells by 10 dpc mouse embryonic skin (Gerschenson et al., 1986). Further research is required to elucidate the final fate of melanoma cells in mammalian embryos and the details of the signaling pathways underlying tumor growth regulation. Understanding regulation of melanoma cells by young embryos could represent a starting point for a developmental theory of the pathogenesis of melanoma, and for future developments of more physiologically-based anticancer therapies for this and indeed, other types of aggressive tumor.

Alejandro Díez-torreRicardo AndradeCristina EguizábalElixabete LópezJon ArluzeaMargarita SilióJuan Aréchaga http://www.intjdevbiol.com 2009-11-01

How we see organisms and cells depends on the tools at our disposal. For over 150 years, biologists were forced to rely on fixed, dehydrated and stained specimens in order to guess how the living cells could function. It all changed abruptly during the last two decades when the rapid development of novel imaging techniques revolutionized the way scientists look at the structures of life alive.

José RinoJosé BragaRicardo HenriquesMaria Carmo-Fonseca http://www.intjdevbiol.com 2009-11-01

Plant development results from specific patterns of gene expression that are tightly regulated in a spatio-temporal manner. Chromatin remodeling plays a central role in establishing these expression patterns and maintaining epigenetic transcriptional states through successive rounds of mitosis that take place within a cell lineage. Plant epigenetic switches occur not only at the embryo stage, but also during postembryonic developmental transitions, suggesting that chromatin remodeling activities in plants can provide a higher degree of regulatory flexibility which probably underlies their developmental plasticity. Here, we highlight recent progress in the understanding of plant chromatin dynamic organization, facilitating the activation or repression of specific sets of genes involved in different developmental programs and integrating them with the response to environmental signals. Chromatin conformation controls gene expression both in actively dividing undifferentiated cells and in those already fate-determined. In this context, we first describe chromatin reorganization activities required to maintain meristem function stable through DNA replication and cell division. Organ initiation at the apex, with emphasis on reproductive development, is next discussed to uncover the chromatin events involved in the establishment and maintenance of expression patterns associated with differentiating cells; this is illustrated with the complex epigenetic regulation of the Arabidopsis floral repressor FLOWERING LOCUS C (FLC). Finally, we discuss the involvement of chromatin remodeling in plant responses to environmental cues and to different types of stress conditions.

José A. JarilloManuel PiñeiroPilar CubasJosé M. Martínez-ZapaterJosé A. JarilloManuel PiñeiroPilar CubasJosé M. Martínez-Zapater http://www.intjdevbiol.com 2009-11-01

Plants, like animals, construct their body following modular sets of instructions that determine cell fate, morphogenesis and patterning, among other building requirements. Hormones regulate plant growth in different ways, and there is increasing evidence for a decisive function of certain hormones in the establishment of developmental programs, equivalent to the role of peptidic molecules and signals of another nature in animal embryo development. Here, we review this role of hormones as instructive agents, and illustrate it with examples such as the generation of morphogenetic gradients by auxin (which determine organ patterning and phyllotaxis), the specification of cell fate at the shoot meristem by gibberellins and cytokinins, the switch between alternative developmental programs (photo- and skotomorphogenesis) by gibberellins and brassinosteroids, and the decision between pistil senescence or fruit growth after anthesis.

David AlabadíMiguel A. BlázquezJuan CarbonellCristina FerrándizMiguel A. Pérez-Amador http://www.intjdevbiol.com 2009-11-01

In order to cope with reproduction in a dry environment without any sort of motility, plants have developed a very specialized and unique sexual system. Of special notice, the two sperm cells that will perform the double fertilization typical of higher plants are carried by one of the fastest growing cells in nature, the pollen tube. This tube develops from the vegetative cell of the pollen grain upon germination on the female tissues. While it cannot be considered as a canonical excitable cell, pollen tubes depend for most of their fundamental functional features on a close regulation of ion dynamics, namely in terms of polarization of extracellular fluxes and formation of standing cytosolic free ion gradients, namely of calcium (Ca2+) and protons (H+). In turn, these imply that plasma membrane transporters are polarized, or polarly regulated, and that internal signaling cascades transduce this spatial information into the basic features of growth and morphogenesis needed for pollen tubes to target correctly the ovules and discharge the sperm cells. Because of the singularity of this organization, and the ease with which pollen tubes can be experimentally handled, recent years have witnessed an accumulation of data at many levels, from basic biophysical and cell biology characterization, to gene assignment and transcriptomic description of pollen development. In this review we aim to organize this information in terms of the basic biophysical features of membrane function and integrate it into conceptual testable hypotheses on how the dynamics of ion regulation may underlie fundamental properties of cell development.

Filipa AlvesErwan MichardJosé A. Feijó http://www.intjdevbiol.com 2009-11-01

Large-scale exploratory approaches to understanding gene function laid the foundations for the “-omics era”. Based on modern technologies for the structural and functional characterization of genomes, these curiosity-driven approaches allow systematic accumulation of vast amounts of data, enabling subsequent hypothesis-driven research. Some years before the dawn of genomics, exploratory approaches were already furthering our understanding of gene function in the form of saturation mutagenesis experiments aimed at the identification of all genes that mutate to a given phenotype. Forward genetic approaches, conducted on experimental organisms such as Drosophila melanogaster and Caenorhabditis elegans, have led to the isolation of mutants affected in specific developmental processes, whose cellular and molecular characterization has unraveled the underlying genetic mechanisms of animal development. To shed light on the making of plant leaves, in 1993 we initiated an attempt to identify as many viable and fertile mutants with abnormal leaf morphology as possible, using the Arabidopsis thaliana model organism. We identified 25 fast-neutron- and 153 ethyl-methane sulfonate-induced mutations, which fell into eight and 94 complementation groups, respectively. We also studied 115 publicly available mutant lines isolated by previous authors, which fell into 37 complementation groups. Although we did not reach saturation of the Arabidopsis thaliana genome, the broad spectrum of leaf morphological alterations identified is facilitating the dissection of specific leaf developmental processes. In a complementary approach, we also analyzed leaf architecture in natural accessions and two populations of recombinant inbred lines. Using a high-throughput gene mapping method, we have already cloned 25 of the genes identified by mutation, in some cases in collaboration with other groups. The products of these genes participate in various developmental processes, such as polar cell expansion, transduction of hormonal signals, gene regulation, plastid biogenesis, and chromatin remodeling, among others. The range of phenotypes and processes identified reveal the complexity of leaf ontogeny and will help explain the diversity of leaf morphology in nature.

José L. MicolMaría R. PonceVíctor QuesadaPedro RoblesHéctor CandelaJose M. Pérez-Pérez http://www.intjdevbiol.com 2009-11-01

Besides being an important commercial crop, tomato (Solanum lycopersicum L.) constitutes a model species for the study of plant developmental processes. Current research tends to combine classic disciplines such as physiology and genetics with modern approaches coming from molecular biology and genomics with a view to elucidating the biological mechanisms underlying plant architecture, floral transition and development of flowers and fruits. Comparative and functional analyses of tomato regulatory genes such as LATERAL SUPPRESSOR (LS), SELF PRUNING (SP), SINGLE FLOWER TRUSS (SFT) and FALSIFLORA (FA) have revealed mechanisms involved in shoot development and flowering time which are conserved among Arabidopsis, tomato and other plant species. Furthermore, several regulatory genes encoding transcription factors have been characterized as responsible for singular features of vegetative and reproductive development of tomato. Thus, the sympodial growth habit seems to require a specific control of the developmental fate followed by shoot meristems. In this process, novel genetic and molecular interactions involving SP, SFT and FA genes would be essential. Also this latter, but mainly ANANTHA (AN) and COMPOUND INFLORESCENCE (S) have recently been found to regulate the inflorescence architecture of the tomato. Concerning fruit development, genetic and molecular analyses of new genes such as fw2.2, FASCIATED, OVATE and SUN have proved their contribution to the domestication process and most importantly, their function as key regulators of fruit size and shape variation. Tomato ripening is also being elucidated thanks to the characterization of regulatory genes such as RIPENING INHIBITOR (RIN), NON-RIPENING (NOR), TDR4 and COLORLESS NON-RIPENING (CNR), which have been found to control early stages of fruit development and maturation. At the same time, much research is dedicated to isolating the targets of the ripening regulators, as well as the key genes promoting the parthenocarpic development of tomato fruits. Hopefully, the ongoing sequencing project and the progress made by integrating several research fields will help to unravel the genetic and molecular pathways controlling tomato development.

Rafael LozanoEstela GiménezBeatriz CaraJuan CapelTrinidad Angosto http://www.intjdevbiol.com 2009-11-01

The development of embryo structures in plants is essential for the formation of the adult plant organs. In cereals, this process has distinct features which have attracted attention from different points of view. Differential gene expression analyses have been used in order to identify genes useful as molecular markers of certain physiological, molecular or developmental processes. Several maize mutants affected in embryo development have been isolated, but only a fraction of them have been characterized at the molecular level. Molecular markers can be useful in the characterization of embryo defective mutants. Here, we describe the different techniques used in the identification of molecular marker genes for embryo development. We describe in more detail some groups of genes coding for cell wall proteins. We also describe the application of these molecular markers in the characterization of some embryo mutants.

Matilde José-EstanyolIgnacio López-RiberaMiriam BastidaTorben JarhmannNuria Sánchez-PonsCristian BecerraCarlos M. VicientPere Puigdomènech