Myosin VI (MYO6) is an actin-based motor that has been implicated in a wide range of cellular processes, including endocytosis and the regulation of actin dynamics. MYO6 is crucial for actin/membrane remodeling during the final step of Drosophila spermatogenesis, and MYO6-deficient males are sterile. This protein also localizes to actin-rich structures involved in mouse spermiogenesis. Although loss of MYO6 in Snell’s waltzer knock-out (KO) mice causes several defects and shows reduced male fertility, no studies have been published to address the role of MYO6 in sperm development in mouse. Here we demonstrate that MYO6 and some of its binding partners are present at highly specialized actin-based structures, the apical tubulobulbar complexes (TBCs), which mediate endocytosis of the intercellular junctions at the Sertoli cell-spermatid interface, an essential process for sperm release. Using electron and light microscopy and biochemical approaches, we show that MYO6, GIPC1 and TOM1/L2 form a complex in testis and localize predominantly to an early endocytic APPL1-positive compartment of the TBCs that is distinct from EEA1-positive early endosomes. These proteins also associate with the TBC actin-free bulbular region. Finally, our studies using testis from Snell’s waltzer males show that loss of MYO6 causes disruption of the actin cytoskeleton and disorganization of the TBCs and leads to defects in the distribution of the MYO6-positive early APPL1-endosomes. Taken together, we report here for the first time that lack of MYO6 in mouse testis reduces male fertility and disrupts spatial organization of the TBC-related endocytic compartment during the late phase of spermiogenesis.

中文翻译：

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肌球蛋白 VI 维持小鼠精子发生过程中内吞作用所需的小管球复合物的肌动蛋白依赖性组织†‡

肌球蛋白 VI (MYO6) 是一种基于肌动蛋白的运动，与广泛的细胞过程有关，包括内吞作用和肌动蛋白动力学的调节。MYO6 在果蝇精子发生的最后一步对肌动蛋白/膜重塑至关重要，而缺乏 MYO6 的雄性是不育的。这种蛋白质也定位于参与小鼠精子发生的富含肌动蛋白的结构。尽管 Snell 的 waltzer 基因敲除 (KO) 小鼠中 MYO6 的缺失会导致一些缺陷并显示雄性生育能力降低，但尚未发表任何研究来解决 MYO6 在小鼠精子发育中的作用。在这里，我们证明 MYO6 和它的一些结合伙伴存在于高度特化的基于肌动蛋白的结构中，顶端小管球复合体 (TBC)，它介导支持细胞 - 精子细胞界面处细胞间连接的内吞作用，精子释放的重要过程。使用电子和光学显微镜和生化方法，我们显示 MYO6、GIPC1 和 TOM1/L2 在睾丸中形成复合物，主要定位于 TBC 的早期内吞 APPL1 阳性隔室，与 EEA1 阳性早期内体不同。这些蛋白质还与 TBC 无肌动蛋白球状区域相关联。最后，我们使用 Snell 的 waltzer 雄性睾丸的研究表明，MYO6 的缺失会导致肌动蛋白细胞骨架的破坏和 TBC 的解体，并导致 MYO6 阳性早期 APPL1 内体的分布缺陷。总之，我们在此首次报告小鼠睾丸中缺乏 MYO6 会降低雄性生育能力，并在精子发生的后期破坏与 TBC 相关的内吞隔室的空间组织。