microchaeta & head
ptcunspecified mutant embryos show severe axon guidance defects. The ventral nerve cord has thickened commissures, indicative of longitudinal tracts abnormally crossing the midline. Breaks are also observed in the longitudinal tracts along with what appears to be the fusing together of the anterior and posterior commissural tracts. These defects are visible in every segment of the embryo.
The medial pathway (as observed with Fas2) is severely affected in ptcunspecified mutant embryos. In approximately 15 hour old ptcunspecified mutant embryos the medial tracts are either collapsed at the midline or are crossing the midline and fasciculating with their contralateral counterpart. These defects are observed in 95% of the hemisegments. In ptcunspecified mutants the entire medial tract either crosses the midline or collapses at the midline. Tracts often fasciculate with each other across the midline. The effect of ptcunspecified on the intermediate and lateral tracts is less severe compared to the medial tract, though it is similar in nature.
In ptcunspecified mutants, in 10-10.5 hour old embryos, the projection of the pCC neuron, which sends out one of the pioneering axons for the medial pathway, either stalls at a position that corresponds to the location of the vMP2 neuron. or projects away from the midline at the vMP2 location. Examination of 11-12 hour old embryos reveals that the medial tract from the posterior hemisegment fails to fasciculate with the medial tract of the anterior hemisegment. Instead the tract crosses the midline and fasciculates with the contralateral tract. Often, the medial tract from one side crosses the midline and projects upwards in the contralateral hemisegment. Defects are also observed in the commissural tracts such as loss of space between the anterior and posterior commissures and the criss-crossing of tracts between the anterior and posterior commissures.
In ptcunspecified mutant embryos, the formation and specification of NB4-2 is affected and as a result the GMC-1-RP2/sib lineage generated from this neuroblast is missing.
Homozygous clones in the wing induced by using Scer\FLP1Scer\UAS.cCa expressed under the control of Scer\GAL4vg.int2.1 can result in phenotypes ranging from duplication of wing vein L3 up to complete anterior/posterior axis duplication.
Egg chambers containing ptcunspecified follicle cell clones contain polar cells at many locations.
Complementary alterations in the number of different midline cells. Midline glia are reduced. No anterior or posterior commissures develop and commissures appear to be fused. In stage 12 mutants commissural axons grow normally toward the midline but appear to stall at the midline.
ptcunspecified mutant embryos show a mirror image duplication of segment boundaries and adjacent cuticle of all segments, with the deletion of the remainder of the segment. These defects are visible during the extended germ band stage.
Tufts of hairs between the antennae and eyes.
ptcunspecified has abnormal neuroanatomy phenotype, suppressible by smoQ4
ptcunspecified has abnormal neuroanatomy phenotype, non-suppressible by sliUAS.cKa/Scer\GAL4sim.PS
ptcunspecified has abnormal neuroanatomy phenotype, non-suppressible by sliUAS.cKa/Scer\GAL4sim.PS/Scer\GAL4UAS.cHa
The induction of sliScer\UAS.cKa under the control of Scer\GAL4sim.PS in a ptcunspecified mutant background does not rescue the ptcunspecified phenotype.
Expression of sliScer\UAS.cKa under the control of the autoregulatory loop Scer\GAL4sim.PS and Scer\GAL4Scer\UAS.cHa in a ptcunspecified mutant background does not rescue the ptcunspecified phenotype.
The guidance defects observed in ptcunspecified mutant embryos are significantly rescued in ptcunspecified smoQ4 double mutants, indicating suppression of the ptcunspecified phenotype by smoQ4. This suggests ptc regulates axon guidance through the repression of smo.
ptcunspecified is rescued by ptcUAS.cMa/Scer\GAL4hs.PB
ptcunspecified is partially rescued by Scer\GAL4arm.PS/ptcUAS.cMa
ptcunspecified is partially rescued by ptct20
ptcunspecified is not rescued by Scer\GAL471B/ptcCΔ.UAS
Maternally-derived expression of ptcScer\UAS.cMa under the control of Scer\GAL4arm.PS in a ptcunspecified mutant background rescues the formation of NB4-2 and specification defects in as many as 60% of hemisegments. With Fas2 staining, guidance defects were rescued in 80% of hemisegments. Staining with BP102 revealed 60% rescue of guidance defects per segment, indicating that not all of the neuroblasts that contribute to commissural tracts were rescued. When Scer\GAL4arm.PS is paternally-derived, neither the NB4-2 defects nor the medial tract guidance defects in ptcunspecified mutants are rescued.
Expression of ptcScer\UAS.cMa under the control of Scer\GAL4hs.PB for 30 minutes at 37oC results in a near complete rescue of the longitudinal tracts in ptcunspecified embryos. Medial tracts are normal in 93% of hemisegments. Even when there is mis-routing of the medal tracts, only a few growth cones appear to be crossing the midline. These rescues are only observed when the ptcScer\UAS.cMa transgene is induced between 2 and 3 hours of development. No rescue is observed with the induction of ptcScer\UAS.cMa during other developmental time points. A 10 minute induction of the ptcScer\UAS.cMa transgene partially rescues the defects, whereas a 20 minute induction results in a very strong rescue. These results indicate that the presence of ptc protein in a narrow time window during the specification of neuroblast identity is sufficient to rescue the medial axon tract defects in ptcunspecified mutant embryos.
Expression of ptcScer\UAS.cMa under the control of the autoregulatory loop Scer\GAL4sim.PS and Scer\GAL4Scer\UAS.cHa in a ptcunspecified mutant background does not rescue the ptcunspecified phenotype.
Expression of ptcScer\UAS.cMa under the control of Scer\GAL4elav-C155 does not rescue the guidance defects observed in ptcunspecified mutant embryos.
