β-Specem6 mutants expressing β-SpecM.Scer\UAS.T:Hsap\MYC under the control of Scer\GAL4elav-C155 are short lived compared to controls.
Heterozygotes show a change in the F-actin network at the larval neuromuscular junction; the meshwork-like organisation around synaptic boutons is lost and the F-actin is instead organised into short and thin wisps/spikes.
β-Specem6/Y embryos display fused anterior and posterior commissures reflecting a reduction in midline repulsion, while β-Specem6/+ embryos exhibit a wild-type ladder-like CNS architecture. In β-Specem6/Y embryos, the medial longitudinal fascicles cross the midline and are closer together than in wild-type embryos. β-Specem6 heterozygotes do not show this aberrant midline crossing. In β-Specem6/Y embryos, one to two Apterous neurons per embryo also aberrantly cross the midline. The initial projection of Apterous neurons is normal at stage at early stages and the midline-crossing defects are observable by late stage 16.
Homozygotes fail to hatch (~90%) or die as early first instar larvae (~10%). Hatched larvae are lethargic and display limited movement. General anatomy of neuromusculature, epidermis, denticles and mouthparts is normal. Morphology of neuromuscular junction, and number of boutons on muscle 6/7 is normal. Mutants have severely reduced synaptic transmission. Evoked EJCs are reduced to approximately one quarter wild type values in voltage clamped muscles. Glutamate response is normal suggesting that the defect is presynaptic. Synaptic transmission is only insignificantly reduced during high-frequency stimulation. However the frequency of sEJCs and mEJCs are significantly reduced, suggesting a Ca2+-independent defect in synaptic vesicle fusion. The amplitude of mEJCs is unaffected, consistent with unaffected postsynaptic receptors. Distribution of active zones and synaptic vesicle clustering is generally normal, though synaptic vesicle density is slightly but significantly reduced. The distribution/polarization of synaptic proteins Syn, Csp, syt, Syx1A dlg1 is distinctly abnormal.
Most hemizygous male embryos die before hatching, although they appear to be fully developed and motile (12 +/- 3% hatch). The mutant larvae survive for 1-3 days, whether or not they hatch. Apicolateral contacts between copper cells and interstitial cells in the midgut are consistently small in wild-type first instar larvae but are large and irregular in hemizygous male first instar larvae. Homozygous larvae show reduced midgut acidification compared to wild-type larvae.
β-Specem6 has abnormal neuroanatomy phenotype, enhanceable by sli2/robo[+]/robo11
β-Specem6, robo[+]/robo11, sli2 has abnormal neuroanatomy phenotype, suppressible | partially by β-SpecUAS.Tag:MYC/Scer\GAL4elav.PLu
β-Specem6 has lethal phenotype, non-suppressible by α-Spec::β-Specα8.Ubi-p63E.Tag:MYC
β-Specem6, sli2 has abnormal neuroanatomy | dominant phenotype, non-suppressible by Scer\GAL4ap-md544/β-SpecUAS.Tag:MYC
β-Specem6 is an enhancer of abnormal neuroanatomy phenotype of robo[+]/robo11, sli2
β-Specem6 is an enhancer of abnormal neuroanatomy | dominant phenotype of sli2
β-Specem6 has medial longitudinal fascicle | ectopic phenotype, enhanceable by sli2/robo[+]/robo11
β-Specem6, robo[+]/robo11, sli2 has medial longitudinal fascicle | ectopic phenotype, suppressible | partially by β-SpecUAS.Tag:MYC/Scer\GAL4elav.PLu
β-Specem6, sli2 has larval neuron phenotype, non-suppressible by Scer\GAL4ap-md544/β-SpecUAS.Tag:MYC
β-Specem6 is an enhancer of medial longitudinal fascicle | ectopic phenotype of robo[+]/robo11, sli2
β-Specem6 is an enhancer of larval neuron phenotype of sli2
Expression of α-Spec::β-Specα8.Ubi-p63E.T:Hsap\MYC fails to suppress lethality found in β-Specem6 mutants, due to its lack of biological activity.
β-Specem6/Y; sli2, robo1/+ show an enhancement of the midline axon guidance defects seen in β-Specem6/Y and sli2, robo1/+ embryos as more medial longitudinal fascicles ectopically cross the midline in the triple mutant. Expression of β-SpecScer\UAS.T:Hsap\MYC, under the control of Scer\GAL4elav.PLu, rescues the phenotype of the triple mutants back to the milder phenotype seen in sli2, robo1/+ embryos.
The Apterous neuron axon guidance phenotype of sli2/+ embryos is enhanced in β-Specem6/Y; sli2/+ embryos, although the timing at which the defects appear is not altered. Expression of β-SpecScer\UAS.T:Hsap\MYC under the control of Scer\GAL4ap-md544 is unable to rescue the β-Specem6/Y; sli2/+ phenotype back to the sli2/+ severity.
β-Specem6 is rescued by Scer\GAL4elav-C155/β-SpecUAS.cMa.Tag:MYC
β-Specem6 is rescued by Scer\GAL4elav-C155/β-SpecUAS.cHa
β-Specem6 is rescued by β-SpecUbi-p63E.Tag:MYC
β-Specem6 is rescued by β-SpecUAS.Tag:MYC/Scer\GAL4elav.PLu
β-Specem6 is rescued by β-SpecUbi-p63E.Tag:MYC
β-Specem6 is partially rescued by β-SpecΔPH.Ubi-p63E.Tag:MYC
β-Specem6 is not rescued by β-SpecUAS.Tag:MYC/Scer\GAL4sim.P3.7
Nervous system expression of β-SpecM.Scer\UAS.T:Hsap\MYC under the control of Scer\GAL4elav-C155 is sufficient to allow a high rate of survival of β-Specem6 males. Reared at 25[o]C, male progeny appear somewhat unhealthy with crumpled wings, rough eyes, small size and are short-lived. Nevertheless, these males are fertile and thus represent a significant rescue of embryonic lethality. At a reduced temperature (22[o]C), the level of β-SpecScer\UAS.T:Hsap\MYC expression is reduced and the appearance of the rescued flies is closer to wild-type (i.e. wings are properly unfolded and the thorax and abdomen are full-size).
Expression of α-Spec::β-Specα13.Ubi-p63E.T:Hsap\MYC rescues the midline axon guidance defects of β-Specem6/Y embryos.
