First Affiliated Hospital of the University of Science and Technology of China, Hefei National Laboratory for Physical Sciences at Microscale, Chinese Academy of Sciences Key Laboratory of Innate Immunity and Chronic Diseases, School of Life Sciences, Chinese Academy of Sciences Center for Excellence in Molecular Cell Science, Collaborative Innovation Center of Genetics and Development, University of Science and Technology of China, Hefei 230027, China.
Department of Cell and Developmental Biology, Biocenter, University of Würzburg, 97074 Würzburg, Germany.
J Biol Chem. 2020 May 8;295(19):6289-6298. doi: 10.1074/jbc.RA119.012375. Epub 2020 Mar 10.
Sperm head shaping is a key event in spermiogenesis and is tightly controlled via the acrosome-manchette network. Linker of nucleoskeleton and cytoskeleton (LINC) complexes consist of Sad1 and UNC84 domain-containing (SUN) and Klarsicht/ANC-1/Syne-1 homology (KASH) domain proteins and form conserved nuclear envelope bridges implicated in transducing mechanical forces from the manchette to sculpt sperm nuclei into a hook-like shape. However, the role of LINC complexes in sperm head shaping is still poorly understood. Here we assessed the role of SUN3, a testis-specific LINC component harboring a conserved SUN domain, in spermiogenesis. We show that CRISPR/Cas9-generated knockout male mice are infertile, displaying drastically reduced sperm counts and a globozoospermia-like phenotype, including a missing, mislocalized, or fragmented acrosome, as well as multiple defects in sperm flagella. Further examination revealed that the sperm head abnormalities are apparent at step 9 and that the sperm nuclei fail to elongate because of the absence of manchette microtubules and perinuclear rings. These observations indicate that deletion likely impairs the ability of the LINC complex to transduce the cytoskeletal force to the nuclear envelope, required for sperm head elongation. We also found that SUN3 interacts with SUN4 in mouse testes and that the level of SUN4 proteins is drastically reduced in null mice. Altogether, our results indicate that SUN3 is essential for sperm head shaping and male fertility, providing molecular clues regarding the underlying pathology of the globozoospermia-like phenotype.
精子头部形态发生是精子发生中的一个关键事件，并且通过顶体-帽网络受到严格控制。核骨架和细胞骨架（LINC）复合物的连接体由 Sad1 和 UNC84 结构域（SUN）和 Klarsicht/ANC-1/Syne-1 同源（KASH）结构域蛋白组成，并形成保守的核膜桥，参与将机械力从帽传递到塑造精子核形成钩状形状。然而，LINC 复合物在精子头部形态发生中的作用仍知之甚少。在这里，我们评估了含有保守 SUN 结构域的睾丸特异性 LINC 成分 SUN3 在精子发生中的作用。我们表明，CRISPR/Cas9 生成的 敲除雄性小鼠不育，精子计数明显减少，表现出类圆头精子症表型，包括顶体缺失、定位错误或碎片化，以及精子鞭毛的多种缺陷。进一步检查表明，精子头部异常在第 9 步明显，并且由于帽微管和核周环的缺失，精子核无法伸长。这些观察结果表明， 缺失可能会损害 LINC 复合物将细胞骨架力传递到核膜的能力，这是精子头部伸长所必需的。我们还发现 SUN3 在小鼠睾丸中与 SUN4 相互作用，并且在缺失小鼠中 SUN4 蛋白水平明显降低。总之，我们的结果表明 SUN3 对于精子头部形态发生和雄性生育力是必不可少的，为类圆头精子症表型的潜在病理学提供了分子线索。
