A TOP6BL mutation abolishes meiotic DNA double-strand break formation and causes human infertility

TOL6BL突变导致减数分裂程序性DNA双链断裂无法产生和人类不孕

Meiosis is pivotal for sexual reproduction and fertility. Meiotic programmed DNA double-strand breaks(DSBs) initiate homologous recombination, ensuring faithful chromosome segregation and generation of gametes. However, few studies have focused on meiotic DSB formation in human reproduction.Here, we report four infertile siblings born to a consanguineous marriage, with three brothers suffering from non-obstructive azoospermia and one sister suffering from unexplained infertility with normal menstrual cycles and normal ovary sizes with follicular activity. An autosomal recessive mutation in TOP6BL was found co-segregating with infertility in this family. Investigation of one male patient revealed failure in programmed meiotic DSB formation and meiotic arrest prior to pachytene stage of prophase I.Mouse models carrying similar mutations to that in patients recapitulated the spermatogenic abnormalities of the patient. Pathogenicity of the mutation in the female patient was supported by observations in mice that meiotic programmed DSBs failed to form in mutant oocytes and oocyte maturation failure due to absence of meiotic recombination. Our study thus illustrates the phenotypical characteristics and the genotype-phenotype correlations of meiotic DSB formation failure in humans.

我们找到一个近亲婚配后代不育家系,该家系有3位非梗阻性无精子症患者和1位原因不明的女性不孕患者.全外显子组测序结合Sanger测序分析发现TOP6BL的c.483dup T突变在该家系中与不孕呈隐性共分离.正常的TOP6BL可与SPO11β结合进而导致减数分裂程序性DNA双链断裂(DSBs)产生,而该突变破坏了二者的结合.对家系中一位男患者的精母细胞进行分析,发现其同源染色体联会异常,减数分裂不能到达粗线期,且染色体轴上缺少减数分裂重组蛋白RPA和DMC1信号,表明其减数分裂程序性DSBs未能产生.我们制备了携带类似患者突变的小鼠,发现突变雄鼠具有与男患者相同的减数分裂异常,突变雌鼠不孕,其卵母细胞中程序性DSBs和减数分裂重组也不能发生,卵母细胞不能成熟.这些发现表明TOP6BL突变可导致人类不孕,为相关不孕不育患者的病因诊断和人工辅助生殖胚胎的遗传检查提供了分子标靶.