Ontogeny and cellular localization of SRY transcripts in the human testes and its detection in spermatozoa

The sex-determining region on the Y (SRY) gene is unequivocally designated as the testis-determining factor in mammals; however, its roles beyond sex determination, if any, have been hitherto unknown. To determine whether SRY has any roles beyond sex determination, herein the expression of SRY mRNA was investigated in the midtrimester human fetal, infantile and adult testes as well as in ejaculated spermatozoa. High levels of SRY transcripts were in situ localized to the Sertoli cells of the developing testis at 9 weeks of gestation, and the expression persisted at comparable levels throughout the midtrimester (until 22 weeks) and also in the testis of an infant at 3 months of age. The germ cells and other somatic cells in the testes of fetuses and the infant were negative for SRY expression. The mRNA for SRY was detected in the spermatogenic cells, particularly the spermatogonia and the round spermatids; the expression was negligible in the meiotic stages. A single transcript of similar to 1.2 kb was detected in the adult testes and isolated spermatogonial cells. In the adult testis, in situ hybridization (ISH) studies revealed a switch in the cellular localization of SRY transcripts. SRY transcripts were also demonstrable by RT-PCR of RNA from ejaculated human spermatozoa. ISH revealed the presence of SRY transcripts in the midpiece of 50% of ejaculated sperm. These results suggest that SRY may have extensive roles in male reproductive physiology, such as maturation of fetal testis, spermatogenesis, sperm maturation and early embryonic development.