Differential expression of early and late embryonic histone genes in adult tissues of the sea urchin Strongylocentrotus purpuratus.

The sea urchin synthesizes distinct classes of histone mRNAs at different stages of development. "Early" embryonic histone mRNAs are synthesized in large amount in cleavage and blastula stage embryos. "Late" embryonic histone mRNAs are the predominant forms in postblastula embryos. To learn more about how early and late histone genes are regulated during the life cycle of the sea urchin and to search for additional classes of developmentally regulated histone mRNAs, we examined histone mRNAs in sea urchin adult tissues. Using methods of primer extension and S1 nuclease protection, we found that tube foot, intestine, testis, and ovary contain a subset of the several H2b mRNA species synthesized by the embryo. We detected early H2b mRNA in ovary, but not in other tissues. Three late H2b mRNA species were present in all tissues tested, while a fourth late H2b was not detected. Using a probe that hybridized specifically with transcripts of a single-copy late H2b gene, we found that this gene was transcribed in both embryos and adults. Interestingly, its level of expression relative to other late H2b genes varied among tissues. Finally, we identified two H2b mRNA species that were distinct from early and late embryonic forms and were synthesized only in adult tissues.