del2/del4 ovarioles contain less developing egg chambers than wild-type. Egg chambers are often smaller than normal and sometimes lack an oocyte. Localization of the oocyte to the posterior pole is also affected. The oocyte is mispositioned in approximately 8% of mutant egg chambers such that it occupies a central or anterior position instead of the normal posterior location. While most older egg chambers in young del2/del4 mutants contain normal numbers of germline cells, younger egg chambers often contain fewer than 16 cells. Of total egg chambers scored, approximately 36% have too few germline cells. Many of these are likely to have resulted from a defect in encapsulation as the missing complement of cells can be found in a neighbouring egg chamber. Oocytes in young females habour fewer than 4 ring canals, in approximately 3% of egg chambers, suggesting that a mitotic defect exists in addition to a defect in encapsulation. A small number of ovarioles in each ovary maintain germline stem cells and these sometimes also contain clusters of germline cells with branched fusomes. From BrdU experiments, the remaining germline stem cells and cystoblasts are found to be mitotically active.
del2/del4 mutants lay few eggs and the eggshells exhibit aberrations indicative of patterning defects along both the anterior-posterior and dorsal-ventral axes. In addition, the eggs are often small and collapsed due to an open chorion at the anterior end. There is variable ventralisation of eggshells indicated by a loss of dorsal appendage material. Most del2/del4 eggs exhibit ventralisation phenotypes ranging from a reduction to a total absence of appendages. Eggshell defects along the anterior-posterior axis are apparent as well. The aeropyle (a respiratory structure) is malformed in the vast majority of all del2/del4 eggs, exhibiting a intermediary morphology between aeropyle and micropyle.
del2/del4 mutants exhibit karyosome defects. The karyosome does not form properly in over 50% of del2/del4 mutant oocytes. DNA staining reveals threadline structures or blobs of staining. In less than 5% of oocytes, chromosomes exhibit polyploidy indicative of a partial loss of oocyte fate.
Approximately 54% of del2/del4 germaria in young females contain several germ cells undergoing apoptosis compared to approximately 2% of controls.
del2/del4 mutant germaria contain at most only one highly-branched fusome instead of 3-4, as observed in wild-type. Instead, large spectrosome-like and barbell-shaped structures accumulate in del2/del4 mutant germaria. These cells do not appear to represent stem cells dislodged from their niche, since their fusome-like structures are larger than stem cell spectrosomes.
del2/del4 mutants exhibit defects in microtubule formation. While most mitotic spindles and microtubule arrays appear normal at a gross level, some abnormalities are observed, such as accumulation of tubulin in early region 1 of germaria. Aberrations in mitotic spindles, most commonly totally collapsed spindles, but occasionally wavy spindles, are also observed.
While the general organisation of microtubule arrays appears normal in del2/del4, there is evidence of failure in focusing minus ends of the array.
del2/del4 males are sterile. Their germline cysts have reduced numbers of highly branched fusomes.