RAPID EVOLUTION IN A CONSERVED GENE FAMILY - EVOLUTION OF THE ACTIN GENE FAMILY IN THE SEA-URCHIN GENUS HELIOCIDARIS AND RELATED GENERA

Camarodont sea urchins possess a rapidly evolving actin gene family wh ose members are expressed in distinct cell lineages in a developmental ly regulated fashion. Evolutionary changes in the actin gene family of echinoids include alterations in number of family members, site of ex pression, and gene linkage, and a dichotomy between rapidly and slowly evolving isoform-specific 3' untranslated regions. We present sequenc e comparisons and an analysis of the actin gene family in two congener ic sea urchins that develop in radically different modes, Heliocidaris erythrogramma and H. tuberculata. The sequences of several actin gene s from the related species Lytechinus variegatus are also presented. W e compare the features of the Heliocidaris and Lytechinus actin genes to those of the the actin gene families of other closely related sea u rchins and discuss the nature of the evolutionary changes among sea ur chin actins and their relationship to developmental mode.