Homozygous embryonic neuromuscular junctions have strongly reduced glutamate-gated currents compared to wild type.

mtg¹ and mtg¹/Df(3R)CA3 mutant neuromuscular junctions show weak/limited glutamate-driven muscle contractions, with a 55% reduction in mean response amplitude.

mtg¹ and mtg¹/Df(3R)CA3 mutant neuromuscular junctions do not display defined excitatory junction currents (EJC) in over 70% of cases. Small and large isolated EJCs are observed in 14% of cases.

Homozygous embryos show a complete absence of movement and failure to hatch. Embryos manually removed from the eggcase show no movement and have a weakened cuticle that is typically accompanied by posterior gut herniation.

Mature embryos are completely paralysed, showing no spontaneous or touch-evoked movement, and show a 100% failure to hatch. The mutant embryos have a normal body anatomy, and a morphologically normal nervous system, musculature and neuromuscular junctions.

Mutant embryos that are manually hatched have a weakened cuticle and posterior gut herniation. A few of these embryos briefly show slight, uncoordinated movement in saline, but no indication of neurally induced body wall peristalsis.

mtg¹/mtg^P2 embryos show limited coordinated movement within the egg case, but they fail to hatch.

Homozygous and mtg¹/Df(3R)CA3 mature embryos have a morphologically normal central nervous system and ventral nerve cord and normal peripheral axon extension, branching and targeting. Neuromuscular junction formation appears normal. Ultrastructurally at the neuromuscular junction, presynaptic bouton morphology and appearance, plasma membrane topology and electron-dense active zones with T-bars appear normal in homozygous and mtg¹/Df(3R)CA3 embryos. There are no significant differences in mean bouton cross-sectional area, mitochondria size or number of synaptic vesicles clustered at the active zone between mutant and control animals. Mutant terminals show a significant increase (33% compared to wild type) in the incidence of plasma membrane cisternae structures and an increase in vesicles docked at the presynaptic membrane. The electron-dense matrix material (which is normally found restricted to the extracellular space between the pre- and post-synaptic membranes) is greatly reduced or absent in mtg¹/Df(3R)CA3 mutants. This phenotype is specific to the cleft matrix domain as normal active zone T-bars are present presynaptically. Post-synaptic polyribosomes are reduced in number and density at more than 65% of the mutant synapses, and are instead often found in dispersed patches, in contrast to the tight packing found in wild-type post-synaptic domains.

Spontaneous excitatory junctional currents (EJCs) are the neuromuscular junction are largely silenced in homozygous and mtg¹/Df(3R)CA3 embryos; occasional spontaneous EJCs are seen, but they display only small amplitudes and patterned bursts of large EJCs are not seen. Evoked transmission at the neuromuscular junction is also severely impaired; approximately 90% of nerve stimuli at homozygous and mtg¹/Df(3R)CA3 neuromuscular junctions result in transmission failure, even with elevated stimulation frequencies, while evoked EJCs have reduced amplitudes (mean evoked amplitude is depressed by more than 90%) and more variable response latencies than at control neuromuscular junctions. Response to glutamate at the neuromuscular junction is reduced in homozygous embryos.

Animals expressing mtg^{dsRNA.Scer\UAS} under the control of Scer\GAL4^elav-C155 in a mtg¹/+ background show reduced larval and adult viability, although substantial numbers of viable adults do survive.