Function And Mechanism Study Of Human Non Obstructive Azoospermia Associated Genes In Drosophila Testes

Male factor infertility affects one-sixth of couples worldwide, and non-obstructive azoospermia (NOA) is one of the most severe forms whose etiology remains largely unknown. Our previous work in a genome-wide association study (GWAS) of NOA in Chinese men, only three loci reached genome-wide significance, although this might be a result of genetic heterogeneity. However, we assume that single nucleotide polymorphisms (SNPs) without genome-wide significance may also indicate genes that are essential for fertility.Here we test promising associations in an extended three-stage validation using 3,608 NOA cases and 5,909 controls to identify 4 additional risk loci. We find one locus approaching genome-wide significance at 1q42.13 (rs3000811, P=7.26x10-8). To test whether this locus affects male fertility, we investigate the phenotypic effect of the related gene (gek, orthologous to CDC42BPA) at 1q42.13 on male fertility using a Drosophila model.To perform large-scale functional screening of the genes surrounding these SNPs, we used in vivo RNA interference (RNAi) in Drosophila, which has a short maturation cycle and is suitable for high-throughput analysis. The analysis found that 7 (31.8%) of the 22 analyzed orthologous Drosophila genes were essential for male fertility. These genes corresponded to nine loci. Of these genes, Lar is primarily required in germ cells to sustain spermatogenesis, whereas CG12404, dmrtllE, CG6769, ERR and sfl function in somatic cells. Interestingly, ERR and sfl are also required for the testis morphogenesis.Azoospermia is a high risk factor of testicular germ cell tumor, the most common cancer in young men, but the underling molecular mechanisms are not clear. In a genome-wide association study trying to identify novel loci associated with human non-obstructive azoospermia (NOA), we uncovered a single nucleotide polymorphism (rsl887102, P=2.60X10-7) in a human gene FOXN3.FOXN3 is an evolutionary conserved gene. We further used Drosophila as a model system to test whether CHES-1-like, the FOXN3 otholog, is required for male fertility. The CHES-1-like knockout flies are viable and fertile and show no defects in spermatogenesis. However, ectopic expression of CHES-1-like in germ cells significantly reduced male fertility. With CHES-1-like overexpressing, the spermatogonia fail to cease mitotic division after four rounds but continue to divide to form tumor like structures. In these testes, the expression levels of differentiation factor Bam were reduced but the expression region of Bam was expanded. Further reduce Bam expression in the CHES-1-like expressing testes enhanced tumor like structure formation. The expression of daughters against dpp (dad), a downstream gene of dpp signaling, was upregulated by CHES-1-like expression in testes. We found that overexpressing CHES-1-like could upregulate dpp expression in wing imaginal discs. In testis, CHES-1-like could directly bind to dpp promoter. We proposed a model that CHES-1-like overexpression in germ cells could upregulate dpp expression and inhibit germ cell differentiation and finally lead to germ cell tumors.Our study thus demonstrates that SNPs without genome-wide significance in GWAS may also provide clues to disease-related genes and therefore warrant functional analysis. These results advance our understanding of the genetic susceptibility to NOA and provide insights into its pathogenic mechanism.