Int. J. Dev. Biol. 58: 533 - 549 (2014)
doi: 10.1387/ijdb.140080nk
© UPV/EHU Press

The Lophotrochozoan TGF-β signalling cassette - diversification and conservation in a key signalling pathway

Nathan J. Kenny1,3, Erica K.O. Namigai1, Peter K. Dearden2, Jerome H.L. Hui3, Cristina Grande4 and Sebastian M. Shimeld*,1

1Evolution and Development Research Group, Department of Zoology, University of Oxford, UK, 2Laboratory for Evolution and Development, Genetics Otago and Gravida, The National Centre for Growth and Development, Biochemistry Department, University of Otago, Aotearoa, New Zealand, 3School of Life Sciences, Chinese University of Hong Kong, Shatin, Hong Kong and 4Departamento de Biología Molecular and Centro de Biología Molecular "Severo Ochoa", CSIC-Universidad Autónoma de Madrid, Madrid, Spain

ABSTRACT TGF-β signalling plays a key role in the patterning of metazoan body plans and growth. It is widely regarded as a ‘module’ capable of co-option into novel functions. The TGF-β pathway arose in the Metazoan lineage, and while it is generally regarded as well conserved across evolutionary time, its components have been largely studied in the Ecdysozoa and Deuterostomia. The recent discovery of the Nodal molecule in molluscs has underlined the necessity of untangling this signalling network in lophotrochozoans in order to truly comprehend the evolution, conservation and diversification of this key pathway. Three novel genome resources, the mollusc Patella vulgata, annelid Pomatoceros lamarcki and rotifer Brachionus plicatilis, along with other publicly available data, were searched for the presence of TGF-β pathway genes. Bayesian and Maximum Likelihood analyses, along with some consideration of conserved domain structure, was used to confirm gene identity. Analysis revealed conservation of key components within the canonical pathway, allied with extensive diversification of TGF-β ligands and partial loss of genes encoding pathway inhibitors in some lophotrochozoan lineages. We fully describe the TGF-β signalling cassette of a range of lophotrochozoans, allowing firm inference to be drawn as to the ancestral state of this pathway in this Superphylum. The TGF-β signalling cascade’s reputation as being highly conserved across the Metazoa is reinforced. Diversification within the activin-like complement, as well as potential wide loss of regulatory steps in some Phyla, hint at specific evolutionary implications for aspects of this cascade’s functionality in this Superphylum.

Keywords:

TGF-β, Lophotrochozoa, BMP, Activin, signalling

*Corresponding author e-mail: sebastian.shimeld@zoo.ox.ac.uk