P{lacZ-un3} is inserted in the 5' untranslated exon of the lbm gene, at position -151bp.
32% of segments lack correct RP3 innervations in homozygous stage 17 embryos.
Mutant embryos show a variable absence of the synapse between RP3 and muscles 7 and 6. Outgrowth of RP3 from the CNS is normal. Synapse formation eventually occurs, but is delayed. No ectopic synapses occur.
Homozygous viable and fertile. Embryonic motor axons follow their appropriate pathways and reach their correct muscle target region by stage early 16, however although they reach their targets, growth cones do not transform into presynaptic terminals in the normal fashion. The RP3 terminal arbor is often absent at stages late 16 and early 17. Also, ectopic axonal arborizations onto muscles 6 and 7 from the transverse nerve form. By the larval stages synapse formation has occurred. Primary defect is impaired ability of the motoneuron growth cone to respond to its muscle targets and transform into a terminal arbor.
