Synaptic currents recorded in Cha^ts2 mutant second instar larvae raised at 18[o]C are significantly reduced.

Averaged synaptic current, recorded in aCC/RP2 neurons, in Cha^ts2 larvae is significantly reduced compared to controls.

Eye photoreceptor axon projection is abberant in late third instar larvae (?) in which the developing retina contains large somatic clones of Cha^ts2 homozygous cells and which have been raised at 30^oC (a non-permissive temperature for this allele). Although the photoreceptor axons enter the optic stalk normally, they sometimes behave abnormally at the exit, and in rare cases form ectopic bundles that miss the lamina target field entirely. Mutant axons that enter the lamina establish an uneven distribution: growth cones fail to form a continuous plexus layer composed of R1-R6 axon termini. However, mistargeted axons do not extend into the medulla target field. Lamina neuronal differentiation and glial migration into the lamina target field is unaffected in these larvae, but these cells are not so precisely organised into distinct glial and neuronal layers as in wild-type. By late pupal stages, photoreceptor axons are segregated properly into lamina and medulla layers, but the projections are somewhat disorganized within each layer.

Mutant embryos raised at 29^oC completely lack EPSCs and sustained currents in aCC/RP2. The arborisation of the aCC, including total area, maximum spread and position relative to the axon scaffold appears normal in these animals. The frequency of presynaptic endings adjacent to aCC remains unchanged compared to wild type. At 29^oC, stimulation of the axons of aCC/RP2 continues to evoke excitatory junctional currents in the target muscles. At 18^oC, the frequency of EPSCs and sustained currents is normal. aCC and RP2 have abnormal electrical properties in mutant embryos raised at 29^oC. The peak current density of both total I_Kfast and I_Na is increased (these alterations are not seen in embryos raised at 18^oC). When mutant embryos are shifted from 18 to 29^oC at early stage 16 and maintained at 29^oC for 5 hours (equivalent to 19 hours after egg laying at 25^oC) they show an increase in the peak current density of I_Kfast in aCC/RP2 (recorded at a time equivalent to 20 hours after egg laying at 25^oC). Embryos returned to 18^oC after 5 hours at 29^oC and allowed to develop show a delay in hatching, and show no significant increase in I_Kfast compared to age-matched controls (recorded at a time equivalent to 23 hours after egg laying at 25^oC).

Cha^ts2/Df(3R)Cha5 flies raised at 18^oC and then transferred to 30^oC can stand and walk around after 1 day at 30^oC. The flies are all paralysed after 2 days at 30^oC.

Monoclonal antibodies to CHA recognise a protein of wild-type molecular weight (80kD) but, even at the permissive temperature, in lesser amounts than in the wild-type.