Meeting Abstract
The Nodal signaling pathway has long been known to pattern left-right asymmetry in deuterostomes. Its absence in ecdysozoans suggested initially that Nodal signaling was a deuterostome innovation. More recently Nodal and its downstream effector Pitx were shown to be conserved in lophotrochozoans, and involved in left-right patterning in mollusk embryos. However, other components of this pathway have so far received little attention, including potential Nodal receptors Alk4 and Alk7, Nodal’s co-ligand Cripto, and components upstream of Pitx. To better understand the evolution of this major pathway in Lophotrochozoa, we examined its role in early embryos of the marine annelid Platynereis dumerilii. We discovered a remarkably well-conserved Nodal signaling cassette. Platynereis embryos exhibit early asymmetric nodal expression followed shortly by pitx. nodal expression is preceded by maternal alk4 and alk7 and zygotic anterior expression of cripto. In addition, we discovered recent gene duplications of cripto, pitx and the Nodal modulator foxh, suggesting greater plasticity of the Nodal signaling casette in Platynereis than in other lophotrochozoans. Together the conservation of Nodal signaling components and recent duplications of core components in Platynereis provides new insights into the evolution of Nodal mediated left-right patterning outside of the deuterostomes.
