Ek. Messersmith et al., SEMAPHORIN-III CAN FUNCTION AS A SELECTIVE CHEMOREPELLENT TO PATTERN SENSORY PROJECTIONS IN THE SPINAL-CORD, Neuron, 14(5), 1995, pp. 949-959
Distinct classes of primary sensory neurons in dorsal root ganglia sub
serve different sensory modalities, terminate in different dorsoventra
l locations in the spinal cord, and display different neurotrophin res
ponse profiles. Large diameter muscle afferents that terminate in the
ventral spinal cord are NT-3 responsive, whereas small diameter affere
nts subserving pain and temperature are NGF responsive and terminate i
n the dorsal spinal cord. Previous in vitro studies showed that the de
veloping ventral spinal cord secretes a diffusible factor that inhibit
s the growth of sensory axons. Here we show that this factor repels NG
F-responsive axons but has little effect on NT-3-responsive axons, We
also provide evidence implicating semaphorin III/collapsin, a diffusib
le guidance molecule expressed by ventral spinal cord cells, in mediat
ing this effect. These results suggest that semaphorin III functions t
o pattern sensory projections by selectively repelling axons that norm
ally terminate dorsally.