α-Speclm88 homozygous and α-Specrg41/α-Speclm88 transheterozygous embryos show mild midline axon guidance defects, with on average less than one medial longitudinal fascicle ectopically crossing the midline per embryo.
Homozygotes fail to hatch (~50%) or die as early first instar larvae (~50%). Hatched larvae are lethargic and display limited movement. General anatomy of neuromusculature, epidermis, denticles and mouthparts is normal, though muscles are slightly thinner than normal and trachea of embryos often remain uninflated. 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 normal. The distribution/polarization of synaptic proteins Syn, Csp, syt, Syx1A dlg1 is distinctly abnormal.
53 +/- 29% of homozygous embryos hatch.
The permeability barrier of the gut of homozygous larvae is intact. Homozygous larvae show significant, but slow, gut motility. There is a lack of acidification in the middle midgut of these larvae.
Females bearing α-Spec mutant clones display dramatically reduced egg laying capacity when mated to wild type males. Ovarioles composed completely of α-Specrg41 contained malformed stage 9 egg chambers and a lack of later stage egg chambers, which accounts for the decreased egg laying frequency. The follicle cell monolayer in stage 9 α-Spec mutant egg chambers is disorganized, with multiple layers of cuboidal follicle cells at the posterior end of the egg chamber and occasionally at the anterior end of the egg chamber. This disruption is due to increased cell division, evident as early as stage 6 egg chambers, not unregulated cell migration. This phenotype is not observed with mutant germline clones, but only when the α-Spec function is lost from the somatic follicle cell layer itself. All other aspects of egg chamber morphology appear normal. The oocyte nucleus occasionally fails to migrate to its dorsal anterior position in stage 9 egg chambers. Mutant germ line clones show fewer than 16 cystocytes in a single egg chamber, similar to the mutant phenotype for hts.
Clones in the ovariole (no α-Spec in the germline) disrupt cyst formation. Egg chambers contain less than 16 cells (but always an even number of cells), often lack an oocyte (egg chambers that contain fewer than 8 cells) and most degenerate before completing oogenesis. Nurse cell cytoplasm is not transferred normally into the oocytes that develop to later stages of oogenesis, resulting in a weak 'dumpless' phenotype. Ring canal formation is normal. Loss of α-Spec in the follicle cells does not disrupt cyst formation. In the germaria some fusome material is often retained in cysts, lack of α-Spec causes a different fusome membrane organisation.
The first larval instar lethality of α-Specrg41 hemizygotes is rescued by α-SpecR22S.RpS27A.T:Hsap\MYC, although the adults produced are lethargic, walk instead of fly, and have reduced fecundity at 19oC and 25oC, and the females cease to lay eggs at 29oC. The egg chambers of α-Specrg41 females carrying α-SpecR22S.RpS27A.T:Hsap\MYC that have been raised at 29oC for 24 hours show discontinuity of the follicle cell monolayer, and contain pycnotic nuclei.
The midgut cells of first instar larvae have disrupted brush border structures. The pore leading into the invaginations is sometimes splayed open, leaving the brush border in direct contact with the midgut lumen, or the pore structures may be extended. Large spaces are seen between the cuprophilic cells and the interstitial cells, and the cuprophilic cells show loss of intracellular organisation. The cell membranes of the interstitial cells show structural alterations. Rescued to the adult stage by α-SpecRpS27A.PL.