LIVINGSTON, BT*; HARMON, M; University of South Florida; University of South Florida: Development of the skeletogenic mesoderm in the Ophiuroid Ophiocoma wendtii

Both sea urchin and brittle star species give rise to embryos and larvae with well developed skeletal spicules, while sea cucumber and sea star embryos have reduced or absent larval skeletons. The uncertain phylogenetic position of brittle stars in relation to the other echinoderm classes makes it unclear whether the similar skeleton in urchins and brittle stars is a shared ancestral trait, or due to convergent evolution. Here we examine the development of the mesoderm in a brittle star, Ophiocoma wendtii, and describe the isolation and characterization of a cDNA encoding a fragment of Alx1 from this species. This gene is involved in the gene regulatory network leading to skeleton formation in sea urchins, and is also expressed in the skeletogenic mesoderm in britte star embryos. The time course of expression of the Alx1 gene in brittle stars is similar to that of sea urchins, although there are differences in the spatial expression pattern that reflect the differences in mesoderm development in brittle stars.