The Y-chromosome-encoded gene RBMY (RNA-binding motif on Y) is a male germline RNA-binding protein and is postulated to be a RNA-splicing regulator. In order to understand the roles of RBMY in different stages of male gamete maturation, the present study aimed at determining its cellular expression during spermatogenesis, spermeogenesis and in mature spermatozoa. In the spermatogonia (cKIT-positive cells), RBMY immunolocalized as two distinct foci, one in the nucleolus and the other in the subnuclear region; in the spermatocytes (cKIT-negative cells), the nucleus had punctuate staining with a subnuclear foci; in the pachytene cells, the protein was localized as a punctuate pattern in the nucleus spread along the elongating chromosomes. In the round and the elongating spermatids, the protein expression was polarized and restricted to the cytoplasm and in the developing mid-piece. In testicular and ejaculated sperm, RBMY was localized to the mid-piece region and weakly in the tail. Incubation of spermatozoa with the RBMY antibody reduced its motility. The spatial differences in expression of RBMY in the germ cells and the presences of this protein in post-meiotic cells and in transcriptionally inert spermatozoa suggest its involvement in multiple functions beyond RNA splicing. One such possible function of RBMY could be its involvement in sperm motility.

Oviductal glycoprotein 1 (OVGP1), also called oviductin, is an oviduct-specific protein and is suggested to play a rolein fertilization. Traditionally, Ovgp1 has been shown to be exclusively expressed by the oviduct; however, recentstudies have demonstrated its expression in some cancers. This observation led us to hypothesize that Ovgp1 mighthave some extra-oviductal expression. In the current study, we evaluated the mRNA and protein expression of Ovgp1in normal reproductive tissues of male and female mice. For the first time, we demonstrate that beyond the oviduct,Ovgp1 mRNA is expressed in the testis, epididymis and ovary, but not in the uterus, cervix, vagina, breast, seminalvesicles and prostate gland. In the testis, Ovgp1 mRNA was localized in the cells at the base of seminiferous tubules(most likely, Sertoli cells), while the protein was detected in the round and elongating spermatids. In the epididymis,Ovgp1 transcripts were localized in epididymal epithelium of the caput but not the corpus and cauda; OVGP1 proteinwas, however, not detected in any of the segments but was present in the epididymal sperm. In the ovary, Ovgp1transcripts and protein were detected in the surface epithelium, granulosa cells of the preantral and the antral folliclesand corpus luteum. In both, the ovary and oviduct, the expression of Ovgp1 was found to be higher at estrus stage thanat diestrus stage. To the best of our knowledge, this is the first study demonstrating the extra-oviductal expression ofOvgp1. Our data suggests that, beyond fertilization, Ovgp1 might have specific roles in gonadal physiology.