Abstract
Drosophila dividing spermatocytes offer a highly suitable cell system in which to investigate the coordinated reorganization of microtubule and actin cytoskeleton systems during cell division of animal cells. Like male germ cells of mammals, Drosophila spermatogonia and spermatocytes undergo cleavage furrow ingression during cytokinesis, but abscission does not take place. Thus, clusters of primary and secondary spermatocytes undergo meiotic divisions in synchrony, resulting in cysts of 32 secondary spermatocytes and then 64 spermatids connected by specialized structures called ring canals. The meiotic spindles in Drosophila males are substantially larger than the spindles of mammalian somatic cells and exhibit prominent central spindles and contractile rings during cytokinesis. These characteristics make male meiotic cells particularly amenable to immunofluorescence and live imaging analysis of the spindle microtubules and the actomyosin apparatus during meiotic divisions. Moreover, because the spindle assembly checkpoint is not robust in spermatocytes, Drosophila male meiosis allows investigating of whether gene products required for chromosome segregation play additional roles during cytokinesis. Here, we will review how the research studies on Drosophila male meiotic cells have contributed to our knowledge of the conserved molecular pathways that regulate spindle microtubules and cytokinesis with important implications for the comprehension of cancer and other diseases.
Highlights
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Fingerhut and Yamashita recently identified novel cytoplasmic ribonucleoprotein (RNP) granules in late spermatocytes that contain mRNAs for the testis-specific axonemal dynein heavy chains, along with the AAA+ (ATPases associated with diverse cellular activities) proteins Reptin and Pontin [44]
The findings in this study propose that the reciprocal dependence between nonmuscle myosin II (NMII) filaments and PI(4)P–GOLPH3 regulate centralspindlin stabilization and contractile ring function during spermatocyte cytokinesis (Figure 3)
Summary
Spermatogenesis is the complex differentiation process that leads to the formation of mature sperms from diploid germ stem cells within the testis. Mature spermatocytes undergo two meiotic divisions in rapid succession, with incomplete cytokinesis, resulting in 64 haploid round spermatids connected by RCs [1,13,14]. Mature spermatocytes undergo two meiotic divisions in rapid succession, with incomplete cytokinesis, resulting in 64 haploid round spermatids. During the G2 phase, the cell volume grows 25-times, while spermatocytes undergo robust gene expression, and the centrioles dock at the plasma membrane, where they assemble short cilia on all four centrioles (light blue). Mature spermatocytes undergo two meiotic divisions in rapid succession, with incomplete cytokinesis, resulting in 64 haploid round spermatids connected by RCs. Following meiosis, all the mitochondria contained in each spermatid fuse to form a complex interlaced structure named the nebenkern.
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