Importin α7 deficiency causes infertility in male mice by disrupting spermatogenesis

Spermatogenesis, a fundamental process in male reproduction, is driven by an ordered series of events, which rely on the trafficking of specific proteins between nucleus and cytoplasm. The importin α family of proteins mediates movement of specific cargo proteins when bound to importin β. Importin α genes have distinct expression patterns in mouse testis, implying they may have unique roles during mammalian spermatogenesis. Here we use a loss-of-function approach to specifically determine the role of importin α7 (Kpna6) in spermatogenesis and male fertility. We show that ablation of importin α7 in male mice leads to infertility and has multiple cumulative effects on both germ cells and Sertoli cells culminating in oligozoospermia. Importin α7-deficient mice exhibit an impaired Sertoli cell function, including loss of Sertoli cells from the seminiferous epithelium and a compromised nuclear transport of the androgen receptor. Furthermore, our data demonstrate devastating defects in spermiogenesis that are accompanied by a disturbed histone-protamine-exchange in elongating spermatids, resulting in incomplete sperm maturation and a massive loss of sperms. Our work uncovers the essential role of importin α7 in spermatogenesis and hence in male fertility. The transcriptomes of testes obtained from Importin α7-/- and α7ΔIBB/ΔIBB mice was compared with those from C57Bl6/N by RNAseq in triplicate

精子发生（spermatogenesis）是雄性生殖的核心生物学过程，由一系列有序事件协同驱动，这些事件依赖于特定蛋白质在细胞核与细胞质之间的转运。输入蛋白α（importin α）家族蛋白在与输入蛋白β（importin β）结合后，可介导特定货物蛋白的跨核质转运。输入蛋白α基因在小鼠睾丸中呈现独特的表达模式，提示其在哺乳动物精子发生过程中可能发挥独特的调控功能。本研究采用功能缺失（loss-of-function）实验策略，特异性解析输入蛋白α7（importin α7，Kpna6）在精子发生与雄性生育能力中的具体作用。研究结果显示，雄性小鼠体内输入蛋白α7的敲除会导致不育，并对生殖细胞与支持细胞（Sertoli cells）产生多种累积性效应，最终引发少精子症。输入蛋白α7缺陷小鼠表现出支持细胞功能受损的表型，具体包括生精上皮（seminiferous epithelium）中支持细胞的丢失，以及雄激素受体（androgen receptor）的核转运功能受损。此外，本研究数据揭示了精子形成（spermiogenesis）过程中存在毁灭性缺陷：该缺陷伴随伸长型精子细胞（elongating spermatids）内组蛋白-鱼精蛋白交换（histone-protamine-exchange）过程的紊乱，最终导致精子成熟不完全以及大量精子丢失。本研究阐明了输入蛋白α7在精子发生乃至雄性生育能力中的关键调控作用。本研究通过RNA测序（RNAseq），对输入蛋白α7基因敲除纯合（Importin α7-/-）以及α7ΔIBB/ΔIBB突变小鼠的睾丸转录组，与C57Bl6/N品系小鼠的睾丸转录组进行了三次生物学重复的比较分析。