Syx473/+ or Syt4BA1/+ third instar larvae do not show significant differences in bouton number at the neuromuscular junction compared to controls, but Syx473/+;Syt4BA1//+ double heterozygotes have significantly fewer boutons compared to controls or either single heterozygote. Syx473/Y;Syt4BA1/Syt4BA1 mutants die during the second instar larval stage. Syx473/+ significantly enhances the reduction in bouton number at the NMJ of Syt4BA1/Syt4BA1 third instar larvae. Syt4BA1/+ does not significantly enhance the reduction in bouton number at the NMJ of Syx473/Y hemizygous third instar larvae.
Syt4BA1/+;Df(3R)Nlg1ex3.1/+ larvae have a significantly reduced ability to grow new "ghost" boutons under high K[+] stimulation at the neuromuscular junction compared to controls and single heterozygotes (though double heterozygotes do not show significant changes in the number of boutons under normal conditions compared to controls).
The synaptic overgrowth (increased number of boutons) at neuromuscular junctions observed in third instar larvae mutant for either cpxSH1 or Syx1A3-69 can be suppressed by homozygosity of Syt4BA1 (which on its own does not lead to any elevation in synaptic growth) but this fails to suppress the increased frequency of mini excitatory junction potentials.
Synaptic outgrowth induced by expression of Syt4wt.Scer\UAS under the control of Scer\GAL4Mhc.PW is dramatically reduced in a parats1 background when animals are reared at 31[o]C compared with 25[o]C.
Like Syt1AD4/Syt1N13 mutants alone, Syt1AD4/Syt1N13, Syt4BA1 double mutants display robust asynchronous release. Paired-pulse facilitation remains intact in the double mutants, with enhanced facilitation as observed in Syt1AD4/Syt1N13 mutants alone. Also similar to Syt1AD4/Syt1N13 mutants alone, the release observed during paired-pulse stimulation in the double mutants remains asynchronous compared to wild type controls.
Syt4GFP-2M or expression of Syt4Scer\UAS.T:Avic\GFP-pHluorinE driven by Scer\GAL4how-24B rescues bouton number at the neuromuscular junction of Syt4BA1/Syt4BA1 third instar larvae; Syt4Scer\UAS.T:Avic\GFP-pHluorinE driven by Scer\GAL4how-24B also rescues ability of mutants to grow new "ghost" boutons under high K[+] stimulation.