Meeting Abstract
We are utilizing the sea urchin as a model system to explore the functional consequence of changes in genes and their cis-regulatory elements during embryonic development. In particular, we are examining genes that are required for development of the larval skeleton. Skeletogenic cells ingress into the blastocoel and form two ventrolateral clusters in response to cues from the overlying ectoderm. These cells then secrete a variety of proteins, which leads to the formation of a pair of triradiate spicules on either side of the archenteron. We are currently focused on the molecular basis of differences in skeletogenesis between derived species and the “primitive” pencil urchin, Eucidaris tribuloides. In derived species, there are two ingression events: the skeletogenic mesenchyme ingresses from the vegetal plate in the early gastrula while the non-skeletogenic mesenchyme ingresses from the tip of the archenteron in the late gastrula. In the pencil urchin, there is just one ingression event with both skeletogenic and non-skeletogenic mesenchyme migrating away from the archenteron during late gastrulation. The snail gene encodes a transcription factor that is required for epithelial-mesenchymal transitions (EMTs) and is known to be upregulated upon ingression in derived species. This gene is also associated with metastasis in humans. Former students isolated this gene from the pencil urchin; we have now performed whole mount in situ hybridization to characterize its expression during embryonic development. In the future, we will study its transcriptional regulation so that we might gain more insight into the initiation of EMT as well as the heterochronic shift in the ingression of the skeletogenic mesenchyme that has occurred during echinoid evolution.
