Retroposition of autosomal mRNA yielded testis-specific gene family on human Y chromosome

Most genes in the human NRY (non-recombining portion of the Y chromosome) c an be assigned to one of two groups: X-homologous genes or testis-specific gene families with no obvious X-chromosomal homologues(1,2). The CDY genes have been localized to the human Y chromosome(1), and we report here that t hey are derivatives of a conventional single-copy gene, CDYL (CDY-like), lo cated on human chromosome 13 and mouse chromosome 6. CDY genes retain CDYL exonic sequences but lack its introns. In mice, whose evolutionary linkeage diverged before the appearance of the Y-linked derivatives, the autosomal Cdyl gene produces two transcripts; one is expressed ubiquitously and the o ther is expressed in testes only. In humans, autosomal CDYL produces only t he ubiquitous transcript; the testis-specific transcript is the province of the Y-borne CDY genes. Our data indicate that CDY genes arose during prima te evolution by retroposition of a CDYL mRNA and amplification of the retro posed gene. Retroposition contributed to the gene content of the human Y ch romosome, together with two other molecular evolutionary processes: persist ence of a subset of genes shared wit the X chromosome(3,4) and transpositio n of genomic DNA harbouring intact transcription units(5).