DAZ family proteins exist throughout male germ cell development and transit from nucleus to cytoplasm at meiosis in humans and mice

The human DAZ gene family is expressed in germ cells and consists of a clus ter of nearly identical DAZ (deleted in azoospermia) genes on the Y chromos ome and an autosomal homolog, DAZL (DAZ-like). Only the autosomal gene is f ound in mice. Y-chromosome deletions that encompass the DAZ genes are a com mon cause of spermatogenic failure in men, and autosomal homologs of DAZ ar e essential for testicular germ cell development in mice and Drosophila. Pr evious studies have reported that mouse DAZL protein is strictly cytoplasmi c and that human DAZ protein is restricted to postmeiotic cells. By contras t, we report here that human DAZ and human and mouse DAZL proteins are pres ent in both the nuclei and cytoplasm of fetal gonocytes and in spermatogoni al nuclei. The proteins relocate to the cytoplasm during male meiosis. Furt her observations using human tissues indicate that, unlike DAZ, human DAZL protein persists in spermatids and even spermatozoa. These results, combine d with findings in diverse species, suggest that DAZ family proteins functi on in multiple cellular compartments at multiple points in male germ cell d evelopment. They may act during meiosis and much earlier, when spermatogoni al stem cell populations are established.