University of Cambridge > > Evolution and Development Seminar Series > Three phases of Wnt signaling define three phases of axis development in the hemichordate S. kowalevskii

Three phases of Wnt signaling define three phases of axis development in the hemichordate S. kowalevskii

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The Wnt signaling pathway is a key regulator of body plan organization and axis formation in all metazoans. We have analyzed the developmental role of Wnt signaling in the hemichordate Saccoglossus kowalevskii to gain insights into deuterostome and bilaterian body plan evolution. Our data suggest that S. kowalevskii is the only known bilaterian retaining the full Wnt complement of the bilaterian ancestor – a characteristic that indicates a slow evolving genome. We have analyzed the roles of Wnt signaling in endomesoderm formation (Darras et al. 2011), axial patterning, and posterior axis elongation. We show that in contrast to chordates where these processes are thought to be linked, in S. kowalevskii these are independent and discreet processes during development. We further show that unlike in chordates where an anterior-posterior Wnt-gradient is being read out for axis specification and patterning, in S. kowalevskii the AP-axis is first divided into three large domains (anterior, center, and posterior) from which surprisingly only the anterior and center domain are specified by Wnt signaling. First after domains are specified is the AP-axis patterned by Wnt signaling, including the posterior. By examining Wnt, Notch signaling and brachyury we further show that posterior axis elongation is not a continuation of initial posterior patterning and gastrulation as proposed for chordates but rather is an independent developmental program identifiable by the rewiring of the posterior network around the time of gastrulation. We discuss the comparative implications of this work for understanding the early evolution of bilaterian axial patterning.

This talk is part of the Evolution and Development Seminar Series series.

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