Cytological analysis of mutant neuroblasts shows that many mutant cells contain anaphase bridges as well as DNA fragments. In order to determine the type of chromosomal aberrations present in these cells, in situ hybridization was performed with centromeric and telomeric probes. Prophase and metaphase cells were observed with very irregular chromosome structure and condensation. These included chromosomes with abnormal condensation patterns and others that did not contain telomeric sequences. Metaphase chromosomes were also observed that appeared to be connected to chromatin masses.
Mutant brains are generally smaller than wild-type brains of similar stages.
Since the mitotic progression of mutant neuroblasts is not delayed and the mitotic indices are only moderately lower than those for wild-type controls, this difference could only be explained by the elevated loss of cells during development. 2 third-instar larval brains were stained for apoptotic cells. The cytological analysis of mutant cells suggests that chromosomes have abnormal condensation patterns. Two specific parameters of chromosome morphology have been analyzed in detail. The length of chromosome arms was measured to assess whether mutant cells are able to shorten the longitudinal axis of chromosomes, and the total number of chromosomes that had clearly defined sister chromatids was also quantified in order to assess whether proper sister chromatid resolution takes place.