Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
Biol Reprod. 2012 Sep 28;87(3):73. doi: 10.1095/biolreprod.112.101980. Print 2012 Sep.
The sperm connecting piece is a complex structure that, from a mechanical perspective, appears to play a role in stabilizing the proximal part of the sperm tail. We report the three-dimensional structure of the intact bovine sperm connecting piece, revealing an intricate, asymmetrical architecture with the segmented columns held together by filamentous linkages. The columns fuse, at the proximal end, with each other into structures that form the centriolar vault, and at the distal end, with the outer dense fibers (ODFs). The grouping of the fibers into these structures is consistent with bending only in the plane of the head. Structures reminiscent of the proximal centriole were observed in the vault, while the association of a novel bar structure with ODFs 3 and 8 organizes the distal centriolar vault. It has been proposed that the elastic compliance of the connecting piece provides the underlying mechanism behind initiation of the sperm beat cycle and bend propagation. According to the basal sliding theory of sperm movement, distortion of the connecting piece may store energy that initiates a new beat. The intersegment linkers could serve as mechanosensitive elements that regulate alternation of the sperm tail's bending direction in the beat cycle in addition to providing structural stabilization for the connecting piece segmented structures. On the other hand, our video recordings of the bull sperm movement show little bending of the head with respect to the tail, so it appears that there may be normally little strain within the connecting piece.
精子连接段是一个复杂的结构，从力学角度来看，它似乎在稳定精子尾部的近端部分中发挥作用。我们报告了完整的牛精子连接段的三维结构，揭示了一种复杂的、不对称的结构，分段的柱状结构通过丝状连接保持在一起。柱状结构在近端与彼此融合，形成中心粒穹顶，在远端与外致密纤维（ODF）融合。这些纤维结构的分组与头部平面内的弯曲一致。在穹顶中观察到类似于近端中心粒的结构，而新型棒状结构与 ODFs3 和 8 的关联组织了远端中心粒穹顶。有人提出，连接段的弹性顺应性为精子拍打周期和弯曲传播的启动提供了潜在机制。根据精子运动的基底滑动理论，连接段的变形可能会储存能量，从而引发新的拍打。连接段分段结构的中间节链接器除了提供结构稳定性外，还可以作为机械敏感元件，调节拍打周期中精子尾部弯曲方向的交替。另一方面，我们对公牛精子运动的视频记录显示头部相对于尾部几乎没有弯曲，因此连接段内的应变似乎通常很小。
