In contrast to most other CNS neurons, midline neurons maintain high levels of Dank2 protein at cell contact sites in neuroglian protein-null embryos. Shown is a comparison of Dank2 immunostaining in the ventral nerve cord of stage 13Drosophila embryos. A depicts a wild-type embryo, whereas the embryo in B does not express neuroglian protein (indicated by the absence of 1B7 mAb, neuroglian-specific immunostaining). Arrowheads indicate groups of midline neuronal cells (VUMs). C depicts the distribution of the neuronal neuroglian form (nrg¹⁸⁰) in the ventral nerve cord at embryonic stage 13. Scale bar, 40 μm.