The Bovine PRAMEY - an Example of Autosome-to-Y-Chromosome Transposition to Enhance Male Reproduction

Autosome-to-Y-chromosome transposition events have been reported in human and several other mammalian species, which are believed to enhance male reproduction. We reported previously the transposition of a gene block from the bovine chromosome 17 to the Y-chromosome approximately 35 million years ago during the bovine evolution. One of the transposed genes was named as PRAMEY, which has been amplified on the bovine Y-chromosome after transposition. Our recent work indicated that PRAMEY is a cancer-testis antigen, and is expressed predominantly in testis and spermatozoa. Copy number of PRAMEY varied from 2 to 30 among 435 bulls (from 15 cattle breeds) investigated with a significant difference among breeds (p<0.05). Association analysis with data from 261 Holstein bulls revealed that CNVs of PRAMEY were correlated significantly with the non-return rate and the semen quality index (p<0.05). The PRAMEY protein were localized predominantly in the acrosome and flagellum of spermatozoa. During spermiogenesis, PRAMEY was highly enriched in and structurally associated with the matrix of acrosomal granule in round spermatids, and migrated with the expansion of the acrosomal granule during acrosomal formation. In addition to the “ER-Golgi-acrosome” biosynthetic transport system, PRAMEY may function in the protein trafficking machinery through the “nucleus-chromatoid body (CB)-organelle” transport system, in which the PRAMEY-labeled CB is frequently associated with the nuclear envelope, and other organelles such as Golgi complex, postacrosomal sheath, perinucleus ring, manchette, centrioles and the developing flagellum, to ensure distribution of material during spermatogenesis. Furthermore, PRAMEY plays a role in sperm function during fertilization.