Ciolfi S, Mencarelli C, Dallai R
Department of Life Sciences, University of Siena, Siena, Italy.
Cytoskeleton (Hoboken). 2016 Apr;73(4):209-18. doi: 10.1002/cm.21291.
The 9 + 2 axoneme of cilia and flagella is specialized machinery aimed at the production of efficient, finely tuned motility, and it has been evolutionarily conserved from protists to mammals. However, the sperm cells of several insects express unconventional axonemes, which represent unique models for studying the structural-functional relationships underlying axonemal function and evolution. Cecidomids comprise a group of dipterans characterized by an overall tendency to deviate from the standard axonemal pattern. In particular, the subfamily Cecidomyiinae shows a series of progressive modifications of the sperm axoneme. We previously analyzed the unusual sperm axonemes of Asphondylia ruebsaameni (Asphondyliidi) and Monarthropalpus buxi (Cecidomyiidi), which are characterized by the absence of any structure related to the control of motility (that is, the central pair complex, radial spokes and inner dynein arms); however, these sperm are motile, and motility is driven by the outer dynein arms only. This simplification of the motility machinery is accompanied by a parallel reduction in the dynein isoform complement. Here, we complete our survey of the axonemal organization and the parallel evolution of sperm dynein complement in cecidomids with the characterization of both the sperm ultrastructure and the dynein genes in Dryomyia lichtensteini, a representative of Lasiopteridi, the cecidomid taxon with aberrant and immotile sperm cells. On the basis of the whole set of our data, we discuss the potential molecular mechanism(s) underlying the progressive modification of axoneme in cecidomids, leading first to a reduction of dynein genes and eventually to the complete loss of motility.
纤毛和鞭毛的9+2轴丝是一种专门用于产生高效、精细调节的运动的机制，并且从原生生物到哺乳动物，它在进化上一直保持保守。然而，几种昆虫的精子细胞表达非常规轴丝，这代表了研究轴丝功能和进化背后的结构-功能关系的独特模型。瘿蚊科包括一组双翅目昆虫，其特征是总体上倾向于偏离标准轴丝模式。特别是，瘿蚊亚科的精子轴丝表现出一系列渐进性的变化。我们之前分析了鲁氏瘿蚊（Asphondyliidi）和布氏单节瘿蚊（Cecidomyiidi）不寻常的精子轴丝，其特征是缺乏与运动控制相关的任何结构（即中央微管对复合体、辐条和内侧动力蛋白臂）；然而，这些精子是可运动的，并且运动仅由外侧动力蛋白臂驱动。这种运动机制的简化伴随着动力蛋白异构体组成的相应减少。在这里，我们通过对李氏瘿蚊（Dryomyia lichtensteini）的精子超微结构和动力蛋白基因进行表征，完成了对瘿蚊科轴丝组织和精子动力蛋白组成的平行进化的研究，李氏瘿蚊是瘿蚊类群毛瘿蚊科的代表，其精子细胞异常且无运动能力。基于我们的全套数据，我们讨论了瘿蚊科轴丝渐进性变化背后的潜在分子机制，这种变化首先导致动力蛋白基因减少，最终导致运动能力完全丧失。
