Genetic dissection of sperm individualization in Drosophila melanogaster.
Genetic dissection of sperm individualization in Drosophila melanogaster.
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发表时间：
1998-05
期刊：
影响因子：
4.6
通讯作者：
J. Fabrizio;G. Hime;S. Lemmon;C. Bazinet
中科院分区：
文献类型：
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作者：
J. Fabrizio;G. Hime;S. Lemmon;C. Bazinet
精子细胞的形态发生通常发生在一个合胞体中，在这个合胞体中，所有从初级精母细胞下来的精子细胞核通过广泛的细胞质桥梁网络保持联系。因此，精子成熟的后期阶段需要将合胞体或包囊物理分解为单个细胞，这一过程有时被称为精子个体化。尽管已经鉴定出果蝇精子细胞个体化的特殊机制(Tokuyasu，K.T.，Peacock，W.J.和Hardy，R.W.(1972)Z.Zellforsch 124,479-506)，以及许多果蝇可突变为雄性不育表型的基因，但人们对完成这种广泛的包囊重塑的机制知之甚少。在这里，个性化复合体的一个主要细胞骨架成分被确认为肌动蛋白，这是一种简单的荧光分析方法。使用罗丹明-鬼臼糖苷作为探针，很容易看到个性化复合体形成在高度拉长的包囊一端的精子细胞核束周围，然后沿着包囊的长度移动。与野生型相比，一个雄性不育的笼状蛋白重链(CHC)突变体的个体化复合体的结构被减少或破坏，这与该突变体缺乏个体化的表型一致。使用荧光分析，其中精子发生进行到高度拉长的囊的组装的雄性不育突变表型的样本区分至少四个不同的表型类：(1)阻止或显著延缓基于肌动蛋白的个性化复合体在核束周围的组装的突变(南京类)，(2)其中个性化复合体在核束内/周围组装，但不能向包囊下移的突变(DUD类)，(3)允许在核束周围组装形态正常的个体化复合体，但在它开始向包囊下移后导致复合体崩溃的突变(MULET类)，和(4)突变(精华类的纯度)，允许组装可移动但形态改变或减少的个体化复合体。在一些核形状改变的突变体中，个体化也失败了，这与精子细胞核为个体化复合体的组装提供了物理支架的假设一致。遗传分析表明，大量具有可用该检测方法区分的表型的额外基因座仍有待鉴定。很大比例的雄性不育突变导致精子发生迟缓，其中高度拉长的包囊未能个体化，这表明这一过程对广泛的细胞扰动具有很大的敏感性。在个体化时所需的大量胞囊细胞质重组被认为是一种相应的复杂功能，需要多种胞质功能的精细协调，这可能解释了先前所述的果蝇基因突变为雄性不育表型的高频率。
The morphogenesis of spermatids generally takes place within a syncytium, in which all spermatid nuclei descended from a primary spermatocyte remain connected via an extensive network of cytoplasmic bridges. A late step in sperm maturation therefore requires the physical resolution of the syncytium, or cyst, into individual cells, a process sometimes referred to as sperm individualization. Despite the identification of specialized machinery involved in the individualization of Drosophila spermatids (Tokuyasu, K. T., Peacock, W. J. and Hardy, R. W. (1972) Z. Zellforsch 124, 479-506), and of many Drosophila genes mutable to male-sterile phenotypes, little is known of the mechanisms by which this extensive remodeling of the cyst is accomplished. Here, the identification of a major cytoskeletal component of the individualization complex as actin is confirmed with a simple fluorescence assay. Using rhodamine-phalloidin as a probe, the individualization complex is readily visualized forming around bundles of spermatid nuclei at one end of highly elongated cysts, then translocating along the length of the cysts. The structure of the individualization complex in a male-sterile clathrin heavy chain (Chc) mutant is observed to be reduced or disrupted relative to wild-type, consistent with the individualization-deficient phenotype of this mutant. Using the fluorescence assay, a sampling of male-sterile mutant phenotypes in which spermatogenesis proceeds to the assembly of highly elongated cysts distinguishes at least four different phenotypic classes: (1) mutations (nanking class) that block or significantly retard the assembly of the actin-based individualization complex around the nuclear bundle, (2) mutations (dud class) in which the individualization complex assembles in/around the nuclear bundle, but fails to translocate down the cyst, (3) mutations (mulet class) that allow the assembly of a morphologically normal individualization complex around the nuclear bundle, but result in a breakdown in the complex after it begins to translocate down the cyst, and (4) mutations (purity of essence class) that allow the assembly of a motile but morphologically altered or reduced individualization complex. Individualization also fails in a number of mutants with altered nuclear shape, consistent with the hypothesis that spermatid nuclei provide a physical scaffolding for the assembly of the individualization complex. Genetic analysis suggests that a substantial number of additional loci with phenotypes distinguishable with this assay remain to be identified. The large proportion of male-sterile mutations resulting in a late block to spermatogenesis, in which highly elongated cysts fail to be individualized, suggest a substantial susceptibility of this process to a broad range of cellular perturbations. The massive reorganization of cyst cytoplasm required at individualization is expected to be a correspondingly complex function requiring exquisite coordination of multiple cytoplasmic functions, and may account for the previously noted high frequency with which Drosophila genes are mutable to male-sterile phenotypes.