STRUCTURE AND EXPRESSION OF NOVEL CLASSES OF HISTONE GENES IN SEA URCHINS

Abstract

There are at least four classes of histone genes expressed in sea urchins in a time dependent and tissue specific fashion. These are the early, the late, the sperm specific and cleavage state histones. In order to elucidate which histone genes are active in adult tissues, the histone messages found in ovary, testis, coelomocytes and muscle of two sea urchin species were analyzed. With the exception of the testis, all tissues contain a subset of the late message variants, though the ratio of messages encoding a particular histone varies. The late genes are therefore somatic genes and are individually regulated in adult tissues. Testis contains late variant H3 and H4 mRNAs, a particular subset of late H2A mRNAs and testis specific H2B and H1 mRNAs. The testis specific H2B and H1 mRNAs are found exclusively in the testis and are larger than the early and late variant messages in accordance with the larger size of sperm H1 and H2B proteins.;Like most histone mRNAs, all of the messages described above are small in size (400 to 800 bases) and are not polyadenylated. A class of larger polyadenylated histone mRNAs has been identified in two sea urchin species. There is at least one poly (A)+ mRNA homologous to each histone type. There is no prototypical pattern of expression of these poly (A)+ mRNAs during development, but the developmental expression profiles of most of these mRNAs are distinct from those of early and late histone mRNAs. The poly (A)+ histone mRNAs are also present in adult tissues. Again, there is no prototypical expression pattern. The tissues contain all or a subset of the poly (A)+ mRNAs found in embryos and usually some additional poly (A)+ histone mRNAs not found in embryos.;The sequence of a gene that encodes a poly (A)+ H1 mRNA was determined. Unlike typical histone mRNAs, the poly (A)+ H1 mRNA has long leader and trailer regions and does not contain the highly conserved palindrome found at the 3{dollar}\sp\prime{dollar} end of most histone mRNAs. This H1 gene encodes a novel H1 protein.;The expression of most histone genes is cell cycle regulated. With analogy to other systems, it is possible that the expression of the sea urchin poly (A)+ histone mRNAs is independent of the cell cycle.