Study On The Role Of NXF3and Crossover Interference In Spermatogenesis

As a major disease, Infertility has a high incidence and affects our health. However, most cases of non-obstructive azoospermia (NOA) remain unexplained and doctor could do nothing for the patients with NOA. Over the past decades, studies indicated that distruption of Blood-testis barrier(BTB) and/or defects in meiotic homologous recombination are the etiological factors underlying spermatogenesis arrest in NOA patients. However, the molecular mechanisms of these defects are currently poorly understood.BTB, constituted by adjacent Sertoli cells in the basal compartment of the seminiferous epithelium, must be disrupted and reassembled to allow the timely passage ofpre-and leptotene permatocytes from the basal compartmen of the seminiferous epithelium, across the BTB, and entering into the adluminal compartment to continue their development. Disruption of the BTB will block the movement of pre-and leptotene permatocytes from the basal compartmen of the seminiferous epithelium and/or allow the production of antisperm antibodies, leading to infertility. It is well known that BTB is regulated by TGF-β3, so we worked for exploring the factor affecting the expression TGF-β3.In this study, we found that mouse NXF3, as one member of Nuclear Export Factor (NXF) family which are implicated in the transport of messenger RNA from the nucleus to the cytoplasm, specifically expressed in Sertoli cells in the mouse testis and the developmental expression coincides well with the formation of BTB between adjacent Sertoli cells. Additionally, NXF3is also specifically expressed in principal cells in the segment II of the caput epididymis and he developmental expression coincides well with the the entry of testicular fluid into the epididymis. Furthermore, A significant negative correlation was found between the levels of TGF-β3and NXF3in the normal mouse testes,and in CdCl2-or heat-treated testes and NXF3was required to mediate TGF-β-induced down-regulation of TGF-33mRNA expression and protein secretion in Sertoli cells. In addition, NXF3was also involved in TGF-β-induced transcriptional regulation of other genes associated with Sertoli cell maturation and the restructuring of the Sertoli cell blood-testis barrier (BTB), such as GATA1, WT1, Claudin11, and p21. The transcriptional regulation of NXF3was mediated through physical interaction with serine-threonine kinase receptor-associated protein (STRAP), where NXF3inhibited the complex formation among Smad7, STRAP and activated type I TGF-β receptor.Homologus Recombination, which ensure the proper segregation of chromosomes during meiosis, occurs between homologous non-sister chromatids in the spermatocytes during meiosis. Homologus Recombination is a complicated process, which includes a double-strand break (DSB) introduced by Spoil, the homologous chromosome invaded by the3’ssDNA tails, generating a Holliday junctions flanking the DSB site and the fomation of crossover (CO). The formation of COs is affected by positive interference, which means that the occurrence of one CO discourages the formation of other COs in its vicinity, so we worked for identifying the characteristic of the crossover interfenrace in human.Immunofluorescence techniques combined with centromere-specific multicolor fluorescence in situ hybridization (cenM-FISH) were employed to identify synaptonemal complexs (SCs) and the COs on SCs in specific chromosomes of pachytene cells. The interference parameter υ estimated by fitting the frequency distribution of inter-CO distances to the gamma model served as measure the strength of CO interference. It was found that CO interference shows significant heterogeneity across the whole genome. For example, there were significant variations intra-chromosomall, inter-chromosomal and inter-individua in the levels of CO interference, with smaller inter-arm and chromosomes COs exhibiting stronger interference than intra-arm and larger chromosomes COs, respectively. Additionally, SCs were found to play an important role in regulating CO interference levels. For example chromosome synapsis anomalies such as discontinuous, regions (gaps) and unsynapsed regions (splits) in chromosome9had both cis and trans effects, on CO interference levels. Furthermore, CO interference was also observed to act continue and uninterrupted by the centromere.