Testicular expression of the mouse histone H1.1 gene

The replication-dependent H1 histone subtype H1.1 is the predominant H1 histone subtype in germ cell chromatin during early spermatogenesis. H1.1 gene transcription was assigned by in situ hybridization with H1.1-specific RNA probes to the basal layer of germ cells within the seminiferous tubule, but not to the somatic cells of the testis. In situ hybridization and immunohistochemistry with testis from 5-, 9-, and 20-day-old mice showed that H1.1 mRNA and protein was already present in spermatogonia of the prepuberal testis. In testis from 20-day-old and adult mice, the H1.1 mRNA remained confined to the most peripheral layer of germ cells. In contrast to the H1.1 mRNA, the H1.1 protein persisted in the germ cell chromatin with decreasing concentration throughout meiosis and in postmeiotic cells. These data demonstrate that in situ hybridization with H1.1 mRNA-specific probes can serve to identify germ cells with ongoing DNA replication. Comparison of results obtained from in situ hybridization and immunocytochemistry indicates that the period of H1.1 gene transcription is restricted to the proliferative phase in which cells undergo successive divisions, whereas the H1.1 protein is a component of the proliferative, meiotic, and spermiogenic phases.