The role of spermatogonially expressed germ cell-specific genes in mammalian meiosis.

Meiosis, a hallmark of sexual reproduction, reduces the chromatin complement by half to cope with genome doubling at fertilization and permits exchange of genetic material between parental genomes. Recent functional studies of novel proteins have greatly enhanced our understanding of the regulation of meiosis. The unique status of sex chromosomes in the male germ line may have shaped their content of germ line-intrinsic genes during evolution. Previously, a unique set of 36 spermatogonially expressed, mouse germ cell-specific genes was identified in one genomic screen. Thirteen of these genes have been disrupted in mice and two-thirds of these mouse mutants exhibit meiotic defects. Therefore, we hypothesize that the majority of uncharacterized germ cell-specific genes identified in the same screen, including 11 X-linked genes, might also play important roles in meiosis. In particular, we cite previously unpublished studies demonstrating that the NXF2 protein, an X-encoded factor, is present in early spermatocytes.