The effect of the floor plate on pattern and polarity in the developing central nervous system.

The effect of floor plate on cellular differentiation in the neural tube of quail embryos was examined. In the developing neural tube the floor plate, which consists of specialized neuroepithelial cells, is located in the ventral midline of the neural tube. When Hensen's node was extirpated the floor plate and notochord did not develop, and the normal differentiation of the ventral horn motor neurons and dorsal and ventral roots did not occur. When one side of the neural tube was deprived of notochord, the ventro-dorsal differentiation took place on both sides. However, when one side of the neural tube was deprived of the floor plate, the ventral horn motor neurons and dorsal and ventral roots did not develop on that side. These observations suggest that the floor plate influences motor neuron differentiation and acts as an intrinsic organizer to establish pattern and polarity in the developing nervous system.