MCZ Lunchtime Seminar

Modulations depending on life history: Wnt signaling in posterior patterning of hemichordate embryos

Lauren Lubeck
PhD candidate
Stanford University

In most classical model systems, the adult body plan is formed directly during embryogenesis, a life history strategy called direct development. However, the life history strategy of most metazoan phyla is indirect, meaning the embryo first becomes a larva and has a body plan radically different to that of the adult. Enteropneust hemichordate worms are a class of marine deuterostomes that contain representatives from both of these life history strategies. In the indirect developing hemichordate, Schizocardium californicum, the larval ectoderm corresponds to the anterior territories of the adult while the posterior, Hox-expressing trunk regions are only added later during metamorphosis. The mechanisms of trunk development have been studied in detail in the direct developing species Saccoglossus kowalevskii and are known to be under the control of Wnt signaling. We hypothesized that the delay in anteroposterior trunk patterning in an indirect developer is controlled by differences in the timing of activation of Wnt signaling. To investigate this possibility, we identified and characterized the expression of components of the Wnt signaling pathway in multiple stages of development in S. californicum and compared these expression patterns with corresponding stages in S. kowalevskii. We treated the S. californicum embryo with a small molecule Wnt signaling activator to identify gene expression changes and chromatin accessibility changes during early AP patterning. These data suggest that the function of Wnt signaling is conserved in inhibiting anterior patterning, but does not promote posterior ectodermal fates in the indirect developing hemichordate.