Geminin is required for mitotic proliferation of spermatogonia

► Geminin is absolutely required for male fertility. ► Geminin(-/-) spermatogonia disappear during the initial wave of mitotic proliferation. ► Geminin(-/-) spermatogonia develop DNA double-stranded breaks. ► Geminin deletion does not alter the pattern of spermatogonial gene expression. ► Geminin is not essential for meiosis or spermiogenesis.