Expression of Sema3D in subsets of neurons in the developing dorsal root ganglia of the rat.

We investigated the expression of the semaphorin family member, Sema3D, in the developing dorsal root ganglia of the rat. Sema3D expression was observed in a subpopulation of dorsal root ganglion (DRG) neurons. The expression peaked at E15 and thereafter it declined. The change in Sema3D expression between E13 and E20 was analyzed by comparison to the expression of TrkA, TrkC and Neuropilin-1 by in situ hybridization. The expression pattern of Sema3D in DRG was similar to that of TrkC and was different from that of TrkA or Neuropilin-1. Double immunohistochemical analysis revealed that Sema3D expression was confined to neurons that expressed TrkC and Runx3, which mediate proprioception, but not to nociceptive neurons that express TrkA. Functionally distinct DRG neurons have different projection patterns in the spinal cord, therefore, Sema3D may regulate the axonal navigation of the large diameter DRG neurons.