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-specific probes corresponding to 3' noncoding termini have been used to characterize their patterns of expression by in situ hybridization. The gene encoding LpC1 actin, which is most similar in sequence to the Strongylocentrotus purpuratus CyI actin, has a complex developmental profile 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 ectoderm of embryos, similarly to the pattern of expression of its closest 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 mesenchyme cells which may be actively engaged in skeletogenesis. Transcripts of the LpM gene accumulate in esophageal muscle cells beginning during gastrulation before overt differentiation. Each of the L. pictus actin genes has a distinct pattern of expression, none of which is identical to that of any S. purpuratus actin gene. These results indicate that 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.