Genetic Variants Of X Chromosome On Spermatogenic Impairment

Infertility has become an important scientific problems in the field of reproductive health.The World Health Organization(WHO)reports that about 10%-15%of couples experience infertility problems,with the man responsible for approximately half of the cases.Spermatogenesis deficiency has become the most common cause of male infertility.Previous studies have suggested that spermatogenesis deficiency is resulted from both environmental and genetic factors and the latter accounts for at least 30%of cases.As males only have a single copy of Y or X chromosome,mutations on Y or X chromosome cannot be compensated by allelic genes,leading to produce phenotypic traits more easily in men.The role of the Y chromosome in spermatogenesis has been well established,while less attention is paid to X chromosome in the process of spermatogenesis.In the history of human evolution,the Y chromosome decreased to?one third the size of the X chromosome and the X chromosome remained more stable in size,suggesting that X chromosome possesses more conserved functions.X chromosome is enriched for germline-specific genes and mutations in X-linked genes can be transmitted for generations through females,without having an influence on reproductive fitness.Therefore,it is wise to screen genes associated spermatogenesis on X chromosome.In this study,we will start with large population association studies,combine the information of X chromosome sequence variants and copy number variants(CNV)of multicopy genes and apply methods in high throughput sequencing(HTS)to investigate the mechanism of X chromosome genetic variations involved in spermatogenesis.Part ?Sequence variants of X chromosome on spermatogenic impairmentNon-obstructive azoospermia(NOA),a severe form of azoospermia characterized by no or little sperm in semen as a result of a congenital dysfunction in spermatogenesis,occurs in approximately 1%of all adult men.Although accumulating evidences demonstrate the critical role of X chromosome in spermatogenesis during the last decades,the expression patterns and potential impact of the X chromosome,together with X-linked genes,on male infertility are less well understood.In this study,we performed X chromosome exome sequencing followed by two-stage independent population validation in 1333 NO A cases and 1141 healthy controls.As a result,we firstly identified four low-frequency variants in four genes(BCORL1,MAP7D3,ARMCX4 and H2BFWT)associated with NOA.Functional studies of mouse spermatogonial stem cells(SSCs)revealed that knocking down Bcorl1,Mtap7d3 and Armcx4 influenced SSC-enriched germ cell proliferation,apoptosis and cell cycle in vitro.Collectively,our data indicate that the X-linked genes BCORL1,MAP7D3 and ARMCX4 are associated with NOA and may be involved in regulating SSCs.Our studies provide a new insight into the role of X-linked maternal-inherited genes in spermatogenesis and could improve the diagnosis of men with NOA.Part ? Copy number variants of X-linked genes on spermatogenic impairmentIn recent years,there has been increasing evidence to implicate the participation of X chromosome in the process of spermatogenesis.To uncover the role of X-linked multicopy genes in spermatogenesis,we performed systematic analysis of X-linked gene copy number variations and Y chromosome haplogrouping in 447 idiopathic NOA patients and 485 healthy controls.Intriguingly,the frequency of individuals with abnormal level copies in Variable Charge X-linked(VCX)genes showed significantly different distribution between cases and controls after multiple test correction(P=5.10×10-5).To discriminate the effect of gain/loss copies in these genes,we reanalyzed the frequency distribution of subjects among subdivided groups.Our results demonstrated that individuals with increased copy numbers of nuclear RNA export factor 2(NXF2)(P=9.21×10-8)and VCX(P=1.97×10-4)genes conferred the risk of NOA.High copy number of VCX increased apopotosis levels and regulated the cell cycle.Our study establishes a robust association between the copy number variation of VCX and risk of NOA.