Int. J. Dev. Biol. 58: 521 - 532 (2014)

https://doi.org/10.1387/ijdb.140133cg

Vol 58, Issue 6-7-8

Special Issue: Spiralian Model Systems

Evolution, divergence and loss of the Nodal signalling pathway: new data and a synthesis across the Bilateria

Published: 15 January 2015

Cristina Grande*^,1, José María Martín-Durán², Nathan J. Kenny^3,#, Marta Truchado-García¹ and Andreas Hejnol²

¹Departamento de Biología Molecular and Centro de Biología Molecular "Severo Ochoa" (Consejo Superior de Investigaciones Científicas - Universidad Autónoma de Madrid), Madrid, Spain, ²Sars International Centre for Marine Molecular Biology, University of Bergen, Bergen, Norway and ³ Evolution and Development Research Group, Department of Zoology, University of Oxford, UK

Abstract

Since the discovery that the TGF-? signalling molecule Nodal and its downstream effector Pitx have a parallel role in establishing asymmetry between molluscs and deuterostomes the debate over the degree to which this signalling pathway is conserved across the Bilateria as a whole has been ongoing. Further taxon sampling is critical to understand the evolution and divergence of this signalling pathway in animals. Using genome and transcriptome mining we confirmed the presence of nodal and Pitx in a range of additional animal taxa for which their presence has not yet been described. In situ hybridization was used to show the embryonic expression of these genes in brachiopods and planarians. We show that both nodal and Pitx genes are broadly conserved across the Spiralia, and nodal likely appeared in the Bilaterian stem lineage after the divergence of the Acoelomorpha. Furthermore, both nodal and Pitx mRNA appears to be expressed in an asymmetric fashion in the brachiopod Terebratalia transversa. No evidence for the presence of a Lefty ortholog could be found in the non-deuterostome genomic resources examined. Nodal expression is asymmetric in a number of spiralian lineages, indicating a possible ancestral role of the Nodal/Pitx cascade in the establishment of asymmetries across the Bilateria.

Keywords

Nodal, Pitx, Spiralia, Bilateria, Brachiopoda