Mical^G56/Mical^I666 larval muscles exhibit abnormal actin accumulations.

Mical^G56/Mical^I666 animals have synaptogenic defects, with a decreased length of synaptic innervation.

Surviving Mical^I666/Df(3R)swp2^MICAL adults often have defects in bristle morphology.

In mutant larvae, neuromuscular terminals form bouton clusters along synaptic branches or around nerve entry points, instead of spreading along muscle fibres as in wild-type larvae.

The synaptic territory (the muscle area covered by neuromuscular junctions) of Mical^I666/Mical^K1496 larvae contains clumps of densely packed boutons, many of which appear smaller.

The neuromuscular junctions of Mical^K583/Mical^I666 embryos do not show any obvious structural differences to wild type. Mical^K583/Mical^I666 first instar larvae have shorter synaptic branches and more clustered boutons at the neuromuscular junction than control larvae.

The number of boutons in the cleft between muscles 6 and 7 is increased compared to controls in homozygous and Mical^I666/Df(3R)swp2^MICAL third instar larvae and the muscle 6+7 surface area is also consistently larger than wild type.

Mical^G56/Mical^I666 adults are strongly flight defective.

Neuromuscular junctions of Mical^G56/Mical^I666 larvae appear structurally more compressed than controls and synaptic boutons aggregate as clusters in the mutants. The sarcomeric patterning normally seen in the somatic muscles is almost completely lost, and clumped boutons are embedded in disordered myosin filaments.

Mical^K583/Mical^I666 third instar larvae show disruption of the sarcomeric patterning normally seen in the somatic muscles, showing misaligned myofilaments. These misaligned myofilaments are located mainly in the peripheral cortex of the muscle fibre and do not, in most cases, extend to the innermost core. The average length of the disorganised filament bundles appears longer than the length of sarcomeres, and the coat of disorganised myofilaments is often interrupted by vessel-like channels (which are derived from terminal tracheal branches). Synaptic boutons of larvae show strong postsynaptic accumulations of filamentous actin (in contrast to wild type) and F-actin also colocalises with the chaotically arranged myosin filaments in the peripheral regions of the muscle.

The overall organisation of the presynaptic terminal at the neuromuscular junction of Mical^K583/Mical^I666 third instar larvae appears ultrastructurally normal. However, there are dramatic changes on the postsynaptic side compared to wild type; the subsynaptic reticulum (SSR) occupies a larger volume around presynaptic boutons and is reduced to small cisternae that are fewer in number and less convoluted than in wild type. The usually highly structured postsynaptic domain is completely disorganised; myofilaments accumulate in postsynaptic regions instead of being strictly separated from the SSR. Myosin-rich thick filaments, often surrounded by associated thin filaments, are seen at the plasma membrane and even directly beneath active zones. The thick filaments are distributed singly or in loose bundles in the cytoplasm and are oriented in all directions. In nearly all cases, boutons are deeply embedded in the muscle tissue and covered with a thick layer of sarcoplasm and disorganised myofilaments.