Schrad Jason R, Fu Gang, Hable Whitney E, Tayar Alexandra M, Oliveira Kenneth, Nicastro Daniela
Department of Cell Biology, University of Texas Southwestern Medical Center, TX 75235.
Biochemistry and Molecular Biotechnology Department, University of Massachusetts Chan Medical School, Worcester, MA 01605.
Mol Biol Cell. 2025 Feb 1;36(2):ar15. doi: 10.1091/mbc.E24-08-0351. Epub 2024 Dec 11.
Cilia and flagella play a crucial role in the development and function of eukaryotes. The activity of thousands of dyneins is precisely regulated to generate flagellar motility. The complex proteome (600+ proteins) and architecture of the structural core of flagella, the axoneme, have made it challenging to dissect the functions of the different complexes, like the regulatory machinery. Previous reports suggested that the flagellum of American eel sperm lacks many of the canonical axonemal complexes yet is still motile. Here, we use cryo-electron tomography for molecular characterization of this proposed "minimal" motile flagellum. We observed different diameters for the eel sperm flagellum: narrow at the base and wider toward the flagellar tip. Subtomogram averaging revealed the three-dimensional (3D) structure of the eel sperm flagellum. As expected, major complexes were missing, for example, outer dynein arms, radial spokes, and the central pair complex, but we found molecular remnants of most complexes. We also identified bend direction-specific patterns in the inter-DMT distance in actively beating eel sperm flagella and we propose a model for the regulation of dynein activity during their motility. Together, our results shed light on the structure and function of the eel sperm flagellum and provide insight into the minimum requirements for ciliary beating.
纤毛和鞭毛在真核生物的发育和功能中起着至关重要的作用。数千个动力蛋白的活性受到精确调控，以产生鞭毛运动。鞭毛结构核心轴丝的复杂蛋白质组（600多种蛋白质）和结构，使得剖析不同复合体（如调控机制）的功能具有挑战性。先前的报道表明，美洲鳗鲡精子的鞭毛缺乏许多典型的轴丝复合体，但仍具有运动能力。在这里，我们使用冷冻电子断层扫描技术对这种所谓的“最小”运动鞭毛进行分子特征分析。我们观察到鳗鲡精子鞭毛的直径不同：基部较窄，向鞭毛尖端逐渐变宽。亚断层平均技术揭示了鳗鲡精子鞭毛的三维（3D）结构。正如预期的那样，主要复合体缺失，例如，外动力蛋白臂、辐条和中央微管对复合体，但我们发现了大多数复合体的分子残余。我们还在活跃摆动的鳗鲡精子鞭毛的双微管间距离中确定了弯曲方向特异性模式，并提出了一个在其运动过程中调控动力蛋白活性的模型。总之，我们的结果揭示了鳗鲡精子鞭毛的结构和功能，并为纤毛摆动的最低要求提供了见解。
