Int. J. Dev. Biol. PODCAST TEXT
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Comparison of Lim1 expression in embryos of frogs with different modes of reproduction

Michael Venegas-Ferrín, Norihiro Sudou, Masanori Taira and Eugenia M. del Pino

In our laboratory at the School of Biological Sciences of the Pontifical Catholic University of Ecuador, in Quito Ecuador we study the developmental strategies of tropical frogs in comparison with the frog Xenopus laevis to gain insights into the mechanisms of early development. In what follows, I will introduce our article entitled “Comparison of Lim1 expression in embryos of frogs with different modes of reproduction”, published in the “International Journal of Developmental Biology” in 2009.

The dorsal blastopore lip of amphibian embryos, which is the Spemann–Mangold organizer, expresses specific genes,and initiates the development of dorsal axial structures. One of the organizer genes is Xlim1 (also known as Xenopus Lhx1), a highly conserved gene among vertebrates. Its ectopic expression in the ventral blastopore lip of the Xenopus laevis gastrula produces duplication of the dorsal axis. To analyze the expression of Lim1 in different frogs we produced a polyclonal antibody against the protein Lim1. The antibody was raised against the conserved C terminal region of Xenopus laevis Lim1 protein. This antibody, which was developed by our co authors Drs. Masanori Taira and Norihiro Sudou at the University of Tokyo, Japan cross reacted with embryos of the species tested, and gave a specific nuclear signal, which was expected, as the protein Lim1 is a transcription factor.

Embryos of four different frogs were analyzed, besides Xenopus laevis, we studied embryos of the foam-nesting frog, the poison-arrow frog, andof the marsupial frog. Thesefrogs belong into four separate families, and have differences in their modes of reproduction, and developmental rates. The expression of Lim1 in embryos of these frogs was comparable with the Xenopus laevis expression pattern. We observed, however, time differences in the expression pattern. In the mid-gastrula of rapidly developing embryos of Xenopus laevis and foam-nesting frog, the protein Lim1 was simultaneously detected in the prechordal plate, which is the head organizer, and notochord, that corresponds to the trunk organizer. In contrast, only the prechordal plate was Lim1-positive during gastrulation in the slow developing embryos of the poison-arrow frog. In embryos of this frog, the notochord elongated, and became Lim1-positive after closure of the blastopore. Our study reveals that the head and trunk organizers are basically separable, and become dissociated in embryos of the slow developing poison-arrow frog. The comparison indicates differences in the timing of gene expression at the dorsal blastopore lip in frog embryos that develop slowly in comparison with Xenopus laevis.  We invite you to read this article. Thank you very much.