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Repulsive guidance cues can steer neuronal growth cones during development and prevent mature axons from regenerating. We have identified a 100 kd glycoprotein in the chick brain that is a good candidate for a repulsive cue. Since it induces the collapse and paralysis of neuronal growth cones in vitro, we have named it collapsin. It is effective at concentrations of approximately 10 pM. The C-terminal half of collapsin contains a single immunoglobulin-like domain and an additional highly basic region. The N-terminal half of collapsin shares significant homology with fasciclin IV, a growth cone guidance protein in grasshopper. Recombinant collapsin causes sensory ganglion growth cones to collapse but not retinal ganglion cell growth cones. We propose that collapsin could serve as a ligand that guides specific growth cones by a motility-inhibiting mechanism.

We have analyzed the control of two segment-specific features in the central nervous system of Drosophila larvae. One of them is present only in the thoracic ganglia of the larva, where it represents the anlage of the adult leg neuromeres; the other is found in the first abdominal, as well as in the thoracic, ganglia. We show that mutations within the bithorax complex have parallel but independent effects on these neural structures and on the larval epidermis. We also show that the central nervous system is very sensitive to mild perturbations of the bithorax complex, and in particular to haploinsufficiency.