Dallai Romano, Lupetti Pietro, Mencarelli Caterina
Department of Evolutionary Biology, University of Siena, Via A Moro 2, I-53100 Siena, Italy.
Int Rev Cytol. 2006;254:45-99. doi: 10.1016/S0074-7696(06)54002-1.
Hexapod spermatozoa exhibit a great variation in their axoneme structure. The 9+2 pattern organization is present in a few basal taxa and in some derived groups. In most hexapods, a crown of nine accessory microtubules surrounds the 9+2 array, giving rise to the so-called 9+9+2 pattern. This general organization, however, displays a number of modifications in several taxa. In this review, the main variations concerning the number and localization of the accessory tubules, microtubular doublets, central microtubules, dynein arms, and axonemal length are summarized. We discuss the phylogenetic significance of all this structural information as well as the current hypotheses relating the sperm size and sperm polymorphism with reproductive success of some hexapod species. Also described are the biochemical data and the motility patterns which are currently known on some peculiar aberrant axonemes, in light of the contribution these models may give to the comprehension of the general functioning of the conventional 9+2 axoneme. Finally, we summarize methodological developments for the study of axoneme ultrastructure and the new opportunities for the molecular analysis of hexapod axonemes.
六足动物的精子鞭毛在轴丝结构上表现出很大的差异。9+2模式的组织存在于一些基部类群和一些衍生类群中。在大多数六足动物中，九个辅助微管围绕着9+2阵列形成一个冠状结构，产生了所谓的9+9+2模式。然而，这种一般的组织结构在几个类群中表现出一些变化。在这篇综述中，总结了关于辅助微管、微管双联体、中央微管、动力蛋白臂的数量和定位以及轴丝长度的主要变化。我们讨论了所有这些结构信息的系统发育意义，以及目前将精子大小和精子多态性与一些六足动物物种的繁殖成功联系起来的假说。还根据这些模型对理解传统9+2轴丝的一般功能可能做出的贡献，描述了目前已知的一些特殊异常轴丝的生化数据和运动模式。最后，我们总结了轴丝超微结构研究的方法进展以及六足动物轴丝分子分析的新机会。
