(((locus is required for cytokinesis during both neuroblast mitosis and male meiosis. and has been noted previously in mutants at the locus, a gene that encodes a member of the cofilin/ADF family of actin-severing proteins. These observations all indicate that proper actin assembly is necessary for centrosome separation and migration. mutations, cytokinesis, central spindle, contractile ring, profilin, eggs was perturbed by calcium buffer injection, the location of the reforming furrow was dependent on the position of the central spindle rather than the poles. A strong correlation between the Rabbit Polyclonal to NEIL1 spindle midzone and the cleavage plane has also been shown by examination of multipolar mitotic figures in living rat kidney cells (Wheatley and Wang 1996) and in cultured human Gamithromycin cells (Eckley et al. 1997). Moreover, modifications of the spindle midzone microtubules by either nocodazole or taxol result in specific and opposite effects on the organization of actin filaments in the cleavage furrow (Fishkind et al. 1996). Finally, Cao and Wang (1996) have recently obtained direct evidence that this central spindle of rat kidney cells provides the signals that stimulate cytokinesis. By puncturing these cells with a blunted needle, they created perforation barriers between different regions of the spindle and the cortex. Only barriers between the spindle midzone and the cortex suppressed cleavage in the equatorial region facing the perforation. Interestingly, whereas the interzonal microtubules were properly organized in the cleaving region of these cells, they were completely disorganized in the noncleaving part of the cells, suggesting an conversation between central spindle microtubules and the equatorial cortex (Cao and Wang 1996). Our approach to elucidate the mechanisms underlying cytokinesis in animal cells is the identification and molecular characterization of genes that control this process in not only offers well-known advantages for genetic analysis, but also provides unique opportunities for cytological examination of mutant phenotypes in Gamithromycin different cell types (for review, see Giansanti et al. 1996). A cell system that is highly suitable for phenotypic characterization of mutants defective in cytokinesis is usually male meiosis (Cenci et al. 1994; Gunsalus et al. 1995; Williams et al. 1995; Giansanti et al. 1996). The presence of cytokinesis problems in mutant testes is usually readily apparent through effects around the easily recognized products of meiosis, the spermatids (see below). Moreover, cytokinesis defects can be analyzed with exquisite cytological resolution Gamithromycin because of the large size of the spermatocytes. The meiotic spindles of males are correspondingly large and exhibit a prominent central spindle that is pinched in the middle during cytokinesis (Cenci et al. Gamithromycin 1994); these cells also exhibit an actin-based contractile ring around the spindle midzone where pinching occurs (Gunsalus et al. 1995). In this paper we report that mutations in the (gene encodes a profilin, a low molecular weight actin-binding protein that regulates actin polymerization (Cooley et al. 1992). In addition, we observed a simultaneous disruption of both the central spindle and the contractile ring in mutants at the ((Williams et al. 1995) loci, and in meiotic cells treated with cytochalasin B. Together, these results strongly suggest that during male meiosis there is a cooperative conversation between the central spindle microtubules and elements of the actomyosin contractile ring, so that impairment of either of these structures prevents the formation of the other. Results Mutations at the chic locus To isolate mutations affecting meiotic cell division in males, we used P-element mutagenesis to generate a collection of autosomal male sterile mutants, and screened these stocks for defects in onion stage spermatids (for the mutagenesis scheme, see Gatti and Goldberg 1991). The morphology of these cells, which consist of a nucleus associated with a mitochondrial derivative called the Nebenkern, is usually diagnostic of errors in chromosome Gamithromycin segregation and/or cytokinesis that occurred during the previous meiotic divisions (Gonzalez et al. 1989; Fuller 1993). We isolated four mutations associated.
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