Importin α proteins play a central role in the transport of cargo from the cytoplasm to the nucleus. In this study, we observed that male knock‐out mice for importin α4, which is encoded by the Kpna4 gene (Kpna4−/−), were subfertile and yielded smaller litter sizes than those of wild‐type (WT) males. In contrast, mice lacking the closely related importin α3 (Kpna3−/−) were fertile. In vitro fertilization and sperm motility assays demonstrated that sperm from Kpna4−/− mice had significantly reduced quality and motility. In addition, acrosome reaction was also impaired in Kpna4−/− mice. Transmission electron microscopy revealed striking defects, including abnormal head morphology and multiple axoneme structures in the flagella of Kpna4−/− mice. A five‐fold increase in the frequency of abnormalities in Kpna4−/− mice compared to WT mice indicates the functional importance of importin α4 in normal sperm development. Moreover, Nesprin‐2, which is a component of the linker of nucleus and cytoskeleton complex, was expressed at lower levels in sperm from Kpna4−/− mice and was localized with abnormal axonemes, suggesting incorrect formation of the nuclear membrane‐cytoskeleton structure during spermiogenesis. Proteomics analysis of Kpna4−/− testis showed significantly altered expression of proteins related to sperm formation, which provided evidence that genetic loss of importin α4 perturbed chromatin status. Collectively, these findings indicate that importin α4 is critical for establishing normal sperm morphology in mice, providing new insights into male germ cell development by highlighting the requirement of importin α4 for normal fertility.

中文翻译：

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importin α4 基因缺失导致精子形态异常并影响小鼠雄性生育能力

Importin α 蛋白在货物从细胞质到细胞核的运输中起核心作用。在这项研究中，我们观察到由 Kpna4 基因 (Kpna4−/−) 编码的 importin α4 的雄性基因敲除小鼠生育力低，与野生型 (WT) 雄性相比，产仔数更小。相比之下，缺乏密切相关的输入蛋白 α3 (Kpna3-/-) 的小鼠可以生育。体外受精和精子活力测定表明，来自 Kpna4-/- 小鼠的精子的质量和活力显着降低。此外，Kpna4-/- 小鼠的顶体反应也受损。透射电子显微镜显示出惊人的缺陷，包括异常头部形态和 Kpna4-/- 小鼠鞭毛中的多个轴丝结构。与 WT 小鼠相比，Kpna4-/- 小鼠的异常频率增加了 5 倍，这表明 importin α4 在正常精子发育中的功能重要性。此外，Nesprin-2 是细胞核和细胞骨架复合体连接体的组成部分，在来自 Kpna4−/− 小鼠的精子中表达水平较低，并且定位于异常轴丝，表明在精子发生。Kpna4-/- 睾丸的蛋白质组学分析显示，与精子形成相关的蛋白质表达显着改变，这提供了导入蛋白 α4 的遗传丢失扰乱染色质状态的证据。总的来说，这些发现表明 importin α4 对于在小鼠中建立正常的精子形态至关重要，