A monoclonal antibody (SN1) identifies a subpopulation of avian sensory neurons whose distribution is correlated with axial level

We have produced a monoclonal antibody, designated SN1, which binds to the surfaces of a subpopulation of avian sensory neurons, but not to other neurons of the peripheral or central nervous systems. The proportion of SN1(+) neurons in brachial and lumbosacral dorsal root ganglia (DRG), which innervate the wings and legs respectively, is low (30-40%), compared to the proportion (80-90%) in the lower thoracic DRG. SN1 immunoreactive fibers project to laminae I and II of the spinal cord dorsal horn, and are seen in the skin, but not the deeper tissues of older embryos. On the basis of the time of appearance, axial level-dependent distribution, and the central and peripheral projections of SN1(+) neurons, we suggest that they are cutaneous afferents that depend on interaction with peripheral targets to differentiate.