Meeting Abstract

P3.91  Monday, Jan. 6 15:30  Isolation of snail and twist from the pencil urchin to gain insight into the heterochronic shift in the ingression of skeletogenic mesenchyme during echinoid evolution. PALMQUIST, A; PAULE, M; ROMANO, L*; Denison University; Denison University; Denison University romanol@denison.edu

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. Skeletogenesis is initiated when the large micromeres are specified to form the larval skeleton. These cells ingress into the blastocoel and form two ventrolateral clusters in response to cues from the overlying ectoderm. They 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 for several differences between “modern” species such as the green urchin, Lytechinus variegatus, and the “primitive” pencil urchin, Eucidaris tribuloides. In modern 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 ingressing from the tip of the archenteron in the late gastrula. We have cloned two genes, snail and twist, from the pencil urchin. These genes are known to be important for the epithelial-mesenchymal transition (EMT) that occurs upon ingression in the green urchin. We are currently examining the transcriptional regulation of these genes to gain insight into the molecular basis of the heterochronic shift in the ingression of the skeletogenic mesenchyme that has occurred during echinoid evolution.