Approximately half the midline glia cells die prematurely in homozygous embryos. In stage 14 homozygous embryos, the midline glia are in their correct final positions at the midline, as in wild-type embryos. By stage 15, one or both commissures may still be incompletely covered and the midline glia have sent out no processes, in contrast to wild-type stage 15 embryos where the glia have completely covered the commissural axons at the midline and have sent out processes to enwrap the commissural axon bundles more ventrally. Lateral to the midline glia cells, the commissural axons in the region between the midline glial cells and the longitudinal tracts are uncovered dorsally in homozygous embryos, in contrast to wild-type where they are almost completely covered by stage 15. At stage 16, the commissural axons of the anterior or posterior commissures are not covered dorsally, owing to the absence of either the MGA or MGP midline glial cells, although the MGM cell is always present. The glial extensions of the midline glial cells in homozygous embryos do not completely enwrap the axon bundles and do not enwrap individual axons or send thin sheet-like processes into the core of the commissures to separate groups of axons, as is seen in wild-type embryos.

Df(3L)H99, wrapper^unspecified has midline glial cell phenotype