Third instar msps^P18/msps^P larval central brains have a significant increase in neuroblast number and mutants also show spindle misorientation in metaphase neuroblasts.

In msps^MJ208/msps^P mutants, no actin overgrowth is observed, even though 100% of oocytes display aberrant hts RNA localisation. Ectopic actin (often in the form of hollow spheres) accumulates in the cytoplasm of these oocytes.

Expression of msps^P under the control of Scer\GAL4^GMR.PF does not affect eye development.

The nucleus is no longer anteriorly positioned after stage 10 in msps^MJ208/msps^P oocytes. Ooplasmic streaming is severely compromised in stage 11 msps^MJ208/msps^P oocytes.

Microtubules are reduced or absent in the ooplasm of msps^MJ208/msps^P egg chambers. These effects are confined largely to the nurse cells during stages 8-9, but microtubules are absent in nurse cells and oocytes by stage 10B.

Haemocytes from mutant larvae show a reduction in the proportion of cells with an extended microtubule array, and a rise in the proportion of cells with a compact circle of microtubules in the centre of the cell. Over 60% of haemocytes have a compact microtubule organisation, compared to 215% in wild-type. Additionally 15% of mutant cells show bundling of microtubules, while none are seen in wild-type.

Microtubule organisation appears normal in many stage 9 msps^P/msps^MJ208 egg chambers. However, some stage 9 msps^P/msps^MJ208 egg chambers have defects in the microtubule cytoskeleton; microtubule density is often reduced in the nurse cells and oocyte and the remaining microtubules appear disorganised. In addition, whereas in wild-type stage 9 follicle cells the density of microtubules is highest at the basal edge of the cell, this polarity is lost in the mutant follicle cells. In wild-type stage 9 and early stage 10 egg chambers, microtubules are seen associated with and extending through the ring canals that link the nurse cells and the oocyte, and these microtubules fan out and form an extensive array in the nurse cell cytoplasm. These microtubules are reduced in density in msps^P/msps^MJ208 egg chambers and they do not form an obvious array in the nurse cell cytoplasm.

Homozygotes die around the larval/pupal transition. Third instar larvae are superficially normal in size and behaviour (they are capable of feeding and crawling) although they grow more slowly than wild type. The animals die before pupation an no development beyond the early pupal stage is seen. The imaginal discs are missing or very small in homozygous third instar larvae and the central nervous system is also reduced in size. Polytenised tissues, such as the salivary glands and fat bodies do not seem to be affected. The degree of chromosome condensation is considerably higher in mitotic cells in the central nervous system of homozygous third instar larvae than in wild type and sister chromatids are attached together at heterochromatic regions. The mitotic index is roughly twice that of wild type, while the frequency of anaphases is very low (only 3% compared to 23.5% in wild type). A quarter of anaphases show V-shaped configurations in which the chromosomes appear to be distributed to three poles. These cells appear to have a diploid component of chromosomes that have undergone separation of sister chromatids. Although one set of sister chromatids moves to one pole, the other set of sister chromatids appear to be divided in their movement to two distinct poles. All chromatids appear to move synchronously and none of the chromosomes are left behind. 2% of cells are polyploid. Only 28% of mitotic cells in the central nervous system of homozygous third instar larvae form an apparently normal bipolar spindle. 36% of mitotic cells contain more than one bipolar spindle. In these cells, most chromosomes are aligned at the metaphase plate and associated with a bipolar spindle, but a few of them have become separated and associate with an additional smaller bipolar spindle. The two bipolar spindles typically sharer one of the poles. In some cases, chromosomes appear still to be aligned on a common metaphase plate even though the spindle has bifurcated and the metaphase plate appears to be kinked. In other cases, a large bipolar spindle is no longer seen, but instead there are multiple small bipolar spindles associated with individual chromosomes. 12% of mitotic cells have one bipolar spindle and one monopolar spindle. 16% of mitotic cells have spindles that have disintegrated so that their exact structure cannot be determined. They contain many short but thick microtubule bundles associated with the chromosome mass.

msps^P, Scer\GAL4^GMR.PF is a suppressor | partially of eye | heat sensitive phenotype of Abl^UAS.cFa, Scer\GAL4^GMR.PF

msps^P, Scer\GAL4^GMR.PF is a suppressor | partially of retina | heat sensitive phenotype of Abl^UAS.cFa, Scer\GAL4^GMR.PF