Echinoderm Body Plan Evolution


BODY PLAN ORIGIN: How did the adult radial body plan evolve from the bilateral ancestral body plan?
APPROACH: Large scale EST sequencing project: three different echinoderm species from 3 different classes. Broad expression study of developmental regulatory genes in each species.
CHOSEN SPECIES: Asteroid – Patiria miniata, Crinoid – Florometra serratissima; Holothuroid – Parastichopus parvimensis.

Echinoderm evolutionEchinoderms – natural experiments in body plans

Echinoderms are one of the most intriguing of the metazoan phyla. As one of the four deuterostome phyla, they are the sister group to hemichordates and closely related to chordates. The extant members are divided into 5 classes, the sea urchins or echinoids, starfish (asteroids), brittle stars (ophiuroids), sea cucumbers (holothuroids), and sea lilies or feather stars (crinoids). The adult body plan of these animals is highly modified and derived in relation to the other deuterostome groups: the most striking element of their body plan is the five-fold radial symmetry; most apparent in the asteroids and ophiuroids. We are interested in the evolutionary steps leading to the transformation of the ancestral bilaterian deuterostome into this unusual and highly modified body plan.

Molecular genetics of the patterning of the adult radial body plan

Many echinoderm species are known for their long-lived planktonic, feeding larvae that feed sometimes for months before metamorphosing into the adult. This larval body plan is often entirely broken down at metamorphosis and the adult formed from a discrete population of cells on the side of the larva. We are interested in the formation of the adult body plan rather than that of the larva, so we have chosen to work on direct-developing species with non-feeding larvae that rapidly develop into adults. We are using our work in hemichordates as a model to characterize the early developmental genetics of adult body patterning asteroid Patiria miniata, the crinoid, Florometra serratissima, and the holothuroid Parastichopus parvimensis. The genome for Patiria will soon be completed by the efforts of a variety of labs, and we have good transcriptome for all three species. We have begun to investigate gene expression in both these species.