The central nervous system of Alk8 mutants appears morphologically normal in terms of segmental nerve branching and segmental muscle patterning. Neuropil synaptic differentiation appears normal in these mutants, with comparable labeling intensity, density and distribution of presynaptic and postsynaptic labels.
Alk8 mutant neuromuscular junctions appear correctly and stereotypically formed and elaborated, with no examples of muscle innervation failure or synaptic targeting errors. Mutant presynaptic active zones appear normally formed and with wild-type size.
R8 axons in mosaic adults with Alk8 in the lamina target neurons exhibit thickened terminals and fasciculate with R7/R8 axons in adjacent columns or fail to extend into the medulla neuropil.
Alk8/+ animals have no observable mutant phenotype.