EXPRESSION OF THE ACTIN GENE FAMILY IN EMBRYOS OF THE SEA-URCHIN LYTECHINUS-PICTUS

The genome of the sea urchin Lytechinus pictus includes genes encoding four cytoskeletal actins LpC1-4 and the muscle actin LpM. Gene-specif ic probes corresponding to 3' noncoding termini have been used to char acterize their patterns of expression by in situ hybridization. The ge ne encoding LpC1 actin, which is most similar in sequence to the Stron gylocentrotus purpuratus CyI actin, has a complex developmental profil e of expression. LpC1 transcripts become prominent in the archenteron and secondary mesenchyme cells of embryos, as well as in adult testis and ovary. The LpC2 actin gene is predominantly expressed in aboral ec toderm of embryos, similarly to the pattern of expression of its close st relatives in S. purpuratus, the SpCyIIIa and SpCyIIIb actin genes. The LpC3 actin gene is expressed at low levels in secondary mesenchyme cells. The LpC4 actin gene is expressed in a subset of primary mesenc hyme cells which may be actively engaged in skeletogenesis. Transcript s of the LpM gene accumulate in esophageal muscle cells beginning duri ng gastrulation before overt differentiation. Each of the L. pictus ac tin genes has a distinct pattern of expression, none of which is ident ical to that of any S. purpuratus actin gene. These results indicate t hat the regulation of expression of members of the actin gene family, even those likely to have common ancestors, has diverged as these sea urchin species diverged. (C) 1994 Academic Press, Inc.