Expression of F84.1/HCA in the developing human spinal cord. The developing human spinal cord was studied using F84.1 MoAb on transverse sections of human embryos, at the trunk level, a 7 weeks postconception. The majority of the motoneurons (mn) of the neural tube have been born and have started to extend axons to form the spinal nerves (sn). Both their cell bodies and axons display strong F84.1 reactivity. At the midline of the neural tube, the floor plate (fp) is also intensely stained. Cell bodies and axons of the DRG neurons that arise from the neural crest also exhibit a strong expression of F84.1 epitope. The central projections of these axons form the dorsal funiculus (df ) in the spinal cord, which is intensely labeled. Nonneuronal tissues such as the notochord and surface ectoderm are also strongly reactive.