elav⁵ mutants affect commissure formation in all neuromeres and lead to a reduction in the number of commissural fibers crossing the CNS midline. The commissural fibers are thinner than in wild-type in 95% of the neuromeres. The posterior commissure is missing entirely in 25% of the neuromeres and both commissures are absent in 5% of the neuromeres. A greater distance between the longitudinal tracts is observed in more than 80% of the neuromeres.

In elav^E476 mutant embryos, EW commissural axons frequently fail to cross the midline and instead grow ipsilaterally (80% of the neuromeres). Similarly, but to a lesser extent, EG commissural axons frequently do not cross the midline, preferentially extending on their own side (>50% of the neuromeres). Contralateral projections were found impaired in 30% of the neuromeres for the SP neurons and no contralateral projections are seen for the RP3 neurons.

Midline glial cells are specified normally and are present in normal numbers and have normal position and morphology in elav^E476 mutant embryos.