The Old World monkey DAZ (Deleted in AZoospermia) gene yields insights into the evolution of the DAZ gene cluster on the human Y chromosome

The DAZ gene cluster on the human Y chromosome is a candidate for the Azoos permia Factor (AZFc). According to the current evolutionary model, the DAZ cluster derived from the autosomal homolog DAZL1 through duplications and r earrangements and is confined to Old World monkeys, apes and humans. To stu dy functional and evolutionary aspects of this gene family we have isolated from a cynomolgus (Old World) monkey testis cDNA library the Y chromosomal cynDAZ and the autosomal cynDAZL1 cDNA, cynDAZL1 contains one DAZ repeat a nd displays high homology to human DAZL1. cynDAZ comprises 11 repeats, each consisting of exons 7 and 8, whereas the human DAZ cDNA repeat units conta in predominantly exon 7, Genomic studies revealed the same amplification ev ents of a 2.4 kb genomic unit encompassing exons 7 and 8 in both species, i ndicating that after splitting of the two lineages, in the human mainly exo n 8 was converted to a pseudoexon by splice site! mutations. The structural features of cynDAZ reveal a move detailed model for the sequence of events reading to the present form of human DAZ. Thus, in a monkey species DAZ is present in a form more ancestral than that of the human. Studies on the im munolocalization of cynDAZ/DAZL1 in cynomolgus monkey testis revealed a bip hasic expression pattern with proteins being detectable in A-pale to B-sper matogonia, late spermatocytes and spermatids, but not in early spermatocyte s and late spermatids, In contrast, in the marmoset monkey, an animal lacki ng DAZ, DAZL1 protein was only expressed in late spermatocytes and early sp ermatids, These findings point to an additional function of cynDAZ/cynDAZL1 during spermatogenesis in the Old World monkey not needed in the New World monkey.