Genetic complementation analysis showed distinct contributions of the N-terminal tail of H2A.Z to epigenetic regulations

H2A.Z is one of the most evolutionally conserved histone variants. In vertebrates, this histone variant has two isoforms, H2A.Z.1 and H2A.Z.2, each of which is coded by an individual gene. H2A.Z is involved in multiple epigenetic regulations, and in humans, it also has relevance to carcinogenesis. In this study, we used the H2A.Z DKO cells, in which both H2A.Z isoform genes could be inducibly knocked out, for the functional analysis of H2A.Z by a genetic complementation assay, as the first example of its kind in vertebrates. Ectopically expressed wild-type H2A.Z and two N-terminal mutants, a nonacetylable H2A.Z mutant and a chimera in which the N-terminal tail of H2A.Z.1 was replaced with that of the canonical H2A, complemented the mitotic defects of H2A.Z DKO cells similarly, suggesting that both acetylation and distinctive sequence of the N-terminal tail of H2A.Z are not required for mitotic progression. In contrast, each one of these three forms of H2A.Z complemented the transcriptional defects of H2A.Z DKO cells differently. These results suggest that the N-terminal tail of vertebrate H2A.Z makes distinctively different contributions to these epigenetic events. Our results also imply that this genetic complementation system is a novel and useful tool for the functional analysis of H2A.Z. For the functional analysis of H2A.Z by a genetic complementation assay, we used the H2A.Z DKO cells, in which both H2A.Z isoform genes could be inducibly knocked out. Similar to wild-type H2A.Z, both of two N-terminal mutants, a nonacetylable H2A.Z mutant and a chimera in which the N-terminal tail of H2A.Z was replaced with that of the canonical H2A, complemented the mitotic defects of H2A.Z-DKO cells; however, each one of these three H2A.Zs (wild-type, the nonacetylable, and chimera of H2A.Z) differed from the other two in complementing the transcriptional defects of H2A.Z DKO cells. These observations suggest that the N-terminal tail of H2A.Z contributes to these epigenetic events in a distinctive manner, and also imply that the genetic complementation system, developed in this study, is suitable for evaluating the roles of functional domains of H2A.Z.