Recent work in sea urchins and Nematostella has shown that activation of Dishevelled (Dsh) proteins in the Wnt/beta-catenin pathway during early embryogenesis plays a critical role in endomesoderm/endoderm segregation. However, the molecular mechanisms underlying this selective activation of Dsh at the vegetal pole of sea urchin embryos and at the animal pole of Nematostella embryos remains poorly understood.
We have recently shown that the unfertilized sea urchin egg cortex contains a specialized domain at the vegetal pole that is marked by the accumulation of high levels of Dsh protein. This domain which we have termed the vegetal cortical domain (VCD) is inherited by the vegetal blastomeres, and recent work by Croce et al. (2011) has shown that the VCD is crucial for the activation of the endomesodermal gene regulatory network during early development. Analysis of Dsh bound to the VCD and in micromeres by 2-Dimensional Western blot analysis has shown that this pool of Dsh has a strikingly different pattern of post-translational modification compared to the pool of Dsh in the rest of the egg/embryo (Peng and Wikramanayake, 2013).
We are currently characterizing the changes seen in the pool of Dsh in the VCD to gain insight into the functional significance of these modifications. We are also using RNA-seq and Dsh co-immunoprecipitation experiments to identify molecular components that tether Dsh to the VCD, and also components that selectively activate this protein in the Wnt/beta-catenin pathway during endomesoderm specification. One goal is to reconstruct the Dsh-binding scaffold in the VCD as this may provide critical insight into how the mechanisms for selectively activating Wnt signaling at one end of the embryo was moved from the animal pole of pre-bilaterians to the vegetal pole in urbilaterians.