mud⁴ mutant third instar larval neuroblasts show mitotic spindle orientation defects, uncoupling the mitotic spindle from the apical-basal polarity axis.

In mud⁴/mud⁴ pupal sensory mother cells, mitotic spindle orientation is parallel to the plane of the epithelium; the orientation of mitotic spindle is also randomized relative to the anterior-posterior axis. In around a quarter of mud⁴/mud⁴ pupal sensory mother cells in telophase, pon fails to exclusively segregate in one of the two daughter cells (pIIb to pIIa cell fate mis-specification): wild type sensory organs are composed of four cells (external socket and shaft, internal neuron and sheath) whereas mud⁴ mutant organs (in pupae 24hr APF) are composed only of external cells.

mud⁴/mud³ mutants have an increased number of brain neuroblasts, and 12-13% of the metaphase neuroblasts show aberrant spindle orientation orthogonal to the apical/basal cortical polarity axis. This subset of neuroblasts showing aberrant spindle orientation always generate equal-sized siblings that both assume neuroblast identity.

Single mud⁴/mud³ neuroblast clones often give rise to two or more neuroblast sibling cells, but never two basal ganglion mother cells.

mud⁴ males exhibit enlarged and misshapen mushroom body structures formed by excessive Kenyon cell proliferation.

mud⁴ females are semi-lethal.

mud⁴ heterozygous flies demonstrate comparable patterns of landmark orientation, indicating similar responses to visual stimulation in Buridan's paradigm as control flies.

mud⁴ heterozygous males exhibit reduced activity levels and walk slower than control flies.

Hemizygous males are fully fertile and produce normal numbers of motile sperm.

Ovaries appear grossly normal in homozygous females. These females lay normal numbers of eggs that have no defects in shape, size or position of the appendages. Eggs laid by mutant females appear to be readily fertilised, but never proceed through normal development to produce hatching larvae.

Homozygous females show no apparent defects in oogenesis; the oocyte is well positioned in the cyst in stage 14 egg chambers, its germinal vesicle has undergone proper migration and condensation and its cytoplasm appears to have received a full contribution from the nurse cells. The meiosis I spindles of the mutant oocytes are indistinguishable from wild type.

The organisation of the meiotic spindles of freshly laid eggs from homozygous females is abnormal; the spindles are disconnected and poorly aligned, with respect to both each other and to the oocyte cortex. In addition, the meiosis II central spindle pole body appears abnormal, with the central ring generally not being observed.

In contrast to wild-type, unfertilised eggs laid by homozygous females do not arrest normally after meiosis, but undergo DNA replication, so that both fertilised and unfertilised eggs laid by mutant females show a gradual proliferation of disorganised chromatin masses. These masses are frequently associated with anastral spindle structures and are sometimes enclosed in a lamin sheath. In some cases, the clumps of DNA appear to have migrated towards the centre of the egg, superficially resembling a cycle 6 or 7 wild-type embryo, but the clumps are not regularly distributed, and the eggs never develop to a recognisable syncytial blastoderm. Eggs derived from mutant females that are 4 hours old typically contain a large number of chromatin masses of varying ploidy spread throughout the egg, while in older eggs, most the the chromatin masses lose coherence and are not associated with a microtubule structure, possibly suggesting DNA breakdown. Some mutant eggs contain clear areas within their cytoplasm, possibly due to necrosis.

mud⁴ mutant flies exhibit hypersensitivity to halothane and enflurane.

Mutant mushroom bodies have a greatly enlarged calyx.

Temperature sensitive mutation. Homozygous flies maintained at 18-20^oC have mushroom body calyces that are nearly normal in size and shape. At 25^oC the calyces are enlarged. The peduncles are distorted, the medial and vertical lobes are reduced and the central complex is moderately distorted under both growth conditions. Heterozygotes have normal brain anatomy. Long and short latency responses are indistinguishable from wild-type flies in both the DLM (flight) and TTM (jump) muscles. EC₅₀ values (the concentration at which half of the long latency responses are expected to fail) for halothane and enflurane for mutant flies are lower than the EC₅₀ values of Canton-S controls, indicating sensitivity to halothane and enflurane. Sensitivity to halothane is codominant. mud¹/mud⁴ flies are sensitive to halothane.

Flies have a number of brain defects, the exact phenotype depending on the genetic background. In the original genetic background in which it was induced, mud⁴ flies have a similar phenotype to mud¹ flies, and the peduncle and lobes are occasionally seen. When placed in a Canton S background, the defects are more severe than in the original genetic background, and the peduncle and lobes are absent.

Semi-lethal.