Axons and glia may be separated by a large amount of extracellular space in mutant third larval instar nerves, in contrast to wild type.
The segmental nerves exhibit a frayed nerve phenotype - localised bulging and swellings are seen i the nerve. This phenotype is 100% penetrant and the defects range from mild bulging to immense bulges that exceed 300μm in length and 50μm in diameter. The number of these bulges range from 8 to 22 per animal. Defasciculated axons are seen within these bulges. There is no strict relation between the presence of a bulge and its location along the nerve. Bulges are found in every nerve and nearly every segment, though there a higher tendency for bulges to occur near the ventral ganglion. For the A8 nerve a second hot spot is found at the levels of segments A6 and A7. Ultrastructural analysis reveals extensive errors in the glial ensheathement of axons, defects that are observed in both the bulging and non-bulging regions of the nerve. The bulging and non-bulging areas exhibit disrupted glial ensheathement. Glial processes that begin to extend circumferentially around the axons fall short of fully wrapping them. The proportion of ensheathing glial processes tha fully encircle the axons in mutants averages only about half in non-bulging compared to 85% in wild-type, though the total length of glial processes in mutants does not differ significantly from wild-type. Other glial errors include sites in the nerve where from three to seven glial processes converge to within half a micron but nevertheless fail to join up with each other. In addition to the glial defects, however the bulging regions contain large electron transparent regions which are presumably filled with fluid. The axons are severely defasciculated. The axons appear normal in number though their average axon diameter is slightly reduced when compared to wild-type. Otherwise all of the cellular components of a normal nerve are present in the bulges. The total length of glial processes appear normal.