Specialized distribution of the histone methyltransferase Ezh2 in the nuclear apical region of round spermatids and its interaction with the histone variant H1t2.

The formation of sperm requires tightly regulated gene expression and unique chromatin remodeling. In the present study, we investigated the spermatogenic distribution of the lysine-specific histone H3 methyltransferase Ezh2 in mice. The distribution of Ezh2 was highly regulated with its localization predominantly restricted to round spermatids in the perinuclear acrosome region. This localization is concomitant with the dramatic epigenetic reorganization that occurs during spermiogenesis leading to an extreme compaction of the chromatin. Spermiogenesis involves the incorporation of sperm-specific nuclear proteins, including the testis-specific histone variant H1t2. Using immunofluorescence, Ezh2 was shown to juxtapose H1t2, and an interaction in chromatin was confirmed by immunoprecipitation. These findings suggest that, in the testis, the apical region of the round spermatid nucleus could be a specialized epigenetic region where methylation of histones serves a role in the spermiogenic chromatin remodeling and that Ezh2 might be a key effector of this event.