Stage-Specific Expression of CYP26B1 in the Adult Testis is Responsible for Pulsatile Retinoic Acid Signaling in Spermatogenesis
Abstract
Seyedmehdi Nourashrafeddin and Batool Hosseini Rashidi
Retinoic acid (RA) plays important roles in spermatogenesis process; however, mechanisms underlying pulsatile RA signaling in meiotic initiation has not been understood yet. We studied expression pattern of RA-degrading enzyme CYP26B1 during development of rhesus monkey testis using qPCR and IHC. In developing monkey testis, the CYP26B1 protein was detected in cytoplasm of undifferentiated spermatogonia. Expression level of CYP26B1 mRNA was down-regulated during testis development which is consistent with initiation of meiosis in adult testis. In adult testes, a heterogeneous pattern of CYP26B1 expression was observed along different stages of seminiferous epithelium, presumably indicates expression pattern of protein is stage specific. Highest level of CYP26B1 protein expression was coincided with onset of meiosis and observed in early meiotic spermatocytes within seminiferous epithelial stages X-XII. Whereas, lowest level of CYP26B1 expression was observed in stages VI-IX of seminiferous epithelium, where undifferentiated Type A spermatogonia divide and differentiate to Type B spermatogonia, meiosis initiates and spermiogenesis occurs. This observations led us to suggest CYP26B1 might be responsible for pulsatile RA signaling in spermatogenesis. Findings presumably support that elevated amount of RA in undifferentiated Type A spermatogonia during stages VI-IX of the seminiferous epithelium of adult monkey testis may be responsible for differentiation of spermatogonia and their meiotic entry