Predominant Expression of Two Bovid-Specific Y-Chromosome Genes (ZNF280BY and PRAMEY) in Spermatids.

Abstract

Autosome-to-Y transposition of male fertility genes is a recurrent theme in mammalian Y-chromosome evolution. As the transposition events occurred separately in different lineages, Y-chromosome genes have been accumulated in the male-specific region (MSY) in a lineage-dependent manner. We have recently discovered two bovid-specific Y-chromosome gene families, Zinc finger protein 280B Y-link (ZNF280BY) and preferentially expressed antigen in melanoma Y-linked (PRAMEY), derived from the transposition of a gene block on the bovine chromosome (BTA) 17. After the transposition, these two gene families were amplified differentially. Over 130 active ZNF280BY loci and 240 ZNF280BY pseudogenes are distributed over the entire MSY region, whereas 16 copies (8 active and 8 pseudogenes) of PRAMEY are present in a small region of MSY on the bovine Y chromosome. Although the function of the ZNF280B/ZNF280BY family is unknown in mammals, the Drosophila ortholog, suppressor of Hairy-wing [Su(Hw)], is a transcriptional regulator and is required for a functional retroviral gypsy insulator. The PRAME/PRAMEY family belongs to the cancer-testis antigens (CTAs) that are predominantly expressed in normal testis and a variety of tumors. PRAME functions as a transcriptional repressor in the retinoic acid receptor (RAR) signaling cascade, and the over-expression of PRAME results in tumorigenesis. Therefore, we hypothesized that ZNF280BY and PRAMEY may play crucial roles in bovine spermatogenesis and male fertility. As the first step to characterize the functions of these two gene families, we analyzed the expression patterns of both families by using RT-PCR, quantitative (q) RT-PCR, cRNA testis section in situ hybridization (ISH) and RNA-deep sequencing approaches. As expected, the expressions of these two Y-chromosome genes are predominant in bovine testes. The RT-PCR analyses revealed that ZNF280BY was expressed predominantly in the testis and slightly in liver, adrenal gland and lymph node, whereas the PRAMEY was expressed specifically in the testis. Furthermore, the sense and antisense RNAs of ZNF280BY and PRAMEY displayed distinct expression patterns both temporally and spatially. ISH with ZNF280BY probes indicated that the ZNF280BY sense RNA was widely expressed, but the antisense RNA was detected only in the spermatids. In contrast, the sense RNA of PRAMEY was expressed specifically in spermatids, whereas the antisense RNA was expressed in all cell types of the seminiferous tubules, with the highest expression in spermatids. qRT-PCR analysis indicated that the expression of ZNF280BY sense RNA increased significantly with age, while the ZNF280BY antisense RNA expression was stable during testis development. For PRAMEY, the expression of the sense RNA was low in 5 to 11-day and 3-month-old testes, but up-regulated in 8-month- and 24-month-old testes; the expression of antisense PRAMEY RNA increased slightly with age. Deep sequencing of the selected cDNAs further suggested that different loci of ZNF280BY and PRAMEY were expressed differentially. Conclusively, our results suggest that the transposed ZNF280BY and PRAMEY families have acquired functional and evolutionary advantages for male spermatogenesis during evolution in cattle. This project was supported by National Research Initiative Competitive Grants no. 2005-35205-18653 and no. 2010-65205-20362 from the USDA National Institute of Food and Agriculture to WSL. (platform)