Involvement of classical bipartite/karyopherin nuclear import pathway components in acrosomal trafficking and assembly during bovine and murid spermiogenesis.

This study arose from our finding that SubH2Bv, a histone H2B variant residing in the subacrosomal compartment of mammalian spermatozoa, contains a bipartite nuclear localization signal (bNLS) but in spite of this did not enter the spermatid nucleus. Instead, it associated with proacrosomic and acrosomic vesicles, which were targeted to the nuclear surface to form the acrosome. On this basis we proposed that SubH2Bv targets proacrosomic/acrosomic vesicles from the Golgi apparatus to the nuclear envelope by utilizing the classical bipartite/karyopherin alpha (KPNA) nuclear import pathway.