Fam9B was associated with human spermatogenesis and male-specific sterility

Abstract

Spermatogenesis is the process of gamete formation, which includes mitosis in spermatogonia, meiosis in spermatocytes, and spermiogenesis. A key event is the formation of the synaptonemal complex (SC). Mutations of genes encoding SC components (such as SYCP3，synaptonemal complex protein 3) lead to infertility or subfertility due to germ cell death. Fam9B mapped on the human chromosome X (Xp22.3) was more similar to SYCP3 in their amino acid sequences and expressed in human testis. However, the expression and precise underlying mechanisms of Fam9B have not been clearly in testes during the spermatogenesis and infertility. And Fam9B mutation associated with sterility? This study was an analysis of azoospermia, sertoli cell only syndrome (SCOS) and proven fertile patients, including 162 patients diagnosed with azoospermia, 65 patients diagnosed with SCOS and 10 proven fertile patients at the Reproductive Medical Center of Peking University Third Hospital between January 2015 and January 2019. Fam9B was cloned, expressed and identified. Genome DNA sequencing analysis, RT-PCR, Western-blot, Immunohistochemistry and immunocytochemistry were performed. Fam9B was analyzed with blood and testicular biopsy samples from azoospermia patients by genome DNA sequencing analysis. These likely mutations were further screened in SCOS patients and in men proven to be fertile. And Fam9B was cloned, expressed and identified with testicular samples using RT-PCR, western blot, Immunohistochemistry and immunocytochemistry. The concentration of testosterone in azoospermia and SCOS patients were determined, and their relativity was studied by statistic methods. Fam9B mRNAs and protein were detected in human testis, and Fam9B was expressed at different level in patients of azoospermia, SCOS and normal groups. Immunohistochemical staining showed that Fam9B was expressed in the nucleus of primary spermatocyte in fertile persons. Moreover, Fam9B was more similar to SYCP3 expression pattern and located on the SC during the leptotene and diplotene spermatocytes. Furthermore, genome DNA sequencing analysis revealed three fam9b deletion patients and five patients of point mutation in fam9b gene. Spermatogenesis of these three patients was arrested at spermatocytes and accompanied by germ cells lost. Interesting, testosterone concentrations levels of these three patients were decreased compared with controls (P < 0.01) . Fam9B may be a SC related protein participated in human normal spermatogenesis. And mutations of fam9b may be risk of spermatocytes arrest and male-specific sterility.