Transmembrane grasshopper Semaphorin I promotes axon outgrowth in vivo.

ABSTRACT

Members of the Semaphorin family of glycoproteins play an important role in axonal pathfinding by functioning as inhibitory guidance cues. Here we provide evidence that a transmembrane form of Semaphorin (Semaphorin I), which is expressed by bands of epithelial cells in the developing grasshopper limb bud, functions as an attractive/permissive cue for the growth cones of the subgenual organ. In addition, we demonstrate that Semaphorin I is needed for initial axonal outgrowth from the subgenual organ. These results are consistent with an alternative function for a transmembrane form of Semaphorin and may explain the previously reported arrest of the proximal extension of the subgenual organ growth cones in the absence of the Ti1 pioneer pathway.