Proper compartmentalization of the sperm flagellum is essential for fertility. The annulus is a septin-based ring that demarcates the midpiece (MP) and the principal piece (PP). It is assembled at the flagellar base, migrates caudally, and halts upon arriving at the PP. However, the mechanisms governing annulus positioning remain unknown. We report that a Chibby3 (Cby3)/Cby1-interacting BAR domain-containing 1 (ciBAR1) complex is required for this process. Ablation of either gene in mice results in male fertility defects, caused by kinked sperm flagella with the annulus mispositioned in the PP. Cby3 and ciBAR1 interact and colocalize to the annulus near the curved membrane invagination at the flagellar pocket. In the absence of Cby3, periannular membranes appear to be deformed, allowing the annulus to migrate over the fibrous sheath into the PP. Collectively, our results suggest that the Cby3/ciBAR1 complex regulates local membrane properties to position the annulus at the MP/PP junction.

中文翻译：

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Cby3/ciBAR1 复合物在精子发生过程中沿着精子鞭毛定位环


精子鞭毛的正确划分对于生育能力至关重要。环带是一个基于隔膜的环，用于划分中段 (MP) 和主段 (PP)。它在鞭毛基部组装，向尾部迁移，并在到达 PP 时停止。然而，控制环带定位的机制仍然未知。我们报告该过程需要 Chibby3 (Cby3)/Cby1 相互作用的 BAR 结构域 1 (ciBAR1) 复合体。小鼠体内任一基因的消融都会导致雄性生育缺陷，这是由精子鞭毛扭结且环在 PP 中错位引起的。 Cby3 和 ciBAR1 相互作用并共定位于鞭毛袋弯曲膜内陷附近的环带。在没有 Cby3 的情况下，环周膜似乎会变形，从而允许环面越过纤维鞘迁移到 PP 中。总的来说，我们的结果表明 Cby3/ciBAR1 复合物调节局部膜特性以将环定位在 MP/PP 连接处。