Testes from Det^Z2775 homozygous males grown at 25[o]C display post-meiotic early (onion stage) spermatids with multiple equal-sized nuclei associated with an enlarged mitochondrial derivative, indicating failure of cytokinesis during both meiotic divisions. Testes from Det^Z2775 homozygous males grown at 29[o]C also exhibit multinucleate spermatids, with 5% of the nuclei varying in size, suggesting defects in both chromosome segregation and cytokinesis in a small number of meiotic divisions. In contrast, onion-stage spermatids from Det^Z2775 homozygous males grown at 18[o]C appear normal, indicating no obvious cytokinesis defects during meiosis.

Hemizygous Det^Z2775/Df(3R)Exel5780 individuals fail to hatch and survive only to larval stages. Spermatids from Det^Z2775/Df(3R)Exel5780 larval males grown at 25[o]C are also multinucleate with an enlarged mitochondria derivative. Chromosomes segregate properly in 83% of Det^Z2775/Df(3R)Exel5780 mutant spermatocytes.

Analysis of mitotic chromosomes in Det^Z2775/Df(3R)Exel5780 larval brain squashes indicate defects in cytokinesis also occur during CNS neuroblast divisions: 23% of metaphase figures are polyploid in the mutant, compared to 0.3% in wild-type. However, the metaphase-to-anaphase transition does not appear to be delayed. The mitotic index is slightly lower than in controls. Analysis of anaphase figures from Det^Z2775/Df(3R)Exel5780 larval neuroblasts fails to detect lagging chromosomes or aberrant chromosome separation to the poles, consistent with defects mainly in cytokinesis rather than in chromosome segregation.

Microtubules in Det^Z2775/Df(3R)Exel5780 mutant spermatocytes extend from the poles and contact the cortex at the equator during anaphase, as in wild-type. Upon initial contact, the microtubules either fail to bundle and stabilize, or do so only transiently. Internal pole-to-equator microtubules fail to organize robust interdigitating arrays at the cell midzone. There is no evidence of furrowing at the equator in Det^Z2775/Df(3R)Exel5780 mutant spermatocytes, and the cells fail to elongate.

Det^Z2775/Df(3R)Exel5780 spermatocytes exhibit a failure of contractile ring formation and constriction. In contrast to spermatocytes, Det^Z2775/Df(3R)Exel5780 neuroblasts exhibit some initial constriction of the cleavage furrow and some irregular bundling of microtubule plus ends in telophase. Despite constriction, completion of cytokinesis is impaired.

The majority of scpo^Z2775 mutant spermatids have one large nebenkern with four nuclei of normal size, indicating a cytokinetic failure in both meiotic divisions. A much smaller proportion have two nuclei and a large nebenkern, indicating failure of only one of the meiotic divisions. Occasionally spermatids are seen (<1% of cases) with more than four nuclei, which may result from defects in the mitotic divisions preceding mitosis. Spermatocytes of scpo^Z2775 mutants lack an organized central spindle and an F-actin ring throughout ana-telophase. The equatorial anillin band is present but fails to constrict properly.