FLOOR PLATE AND MOTOR-NEURON INDUCTION BY DIFFERENT CONCENTRATIONS OFTHE AMINO-TERMINAL CLEAVAGE PRODUCT OF SONIC HEDGEHOG AUTOPROTEOLYSIS

The differentiation of floor plate cells and motor neurons can be indu ced by Sonic hedgehog (SHH), a secreted signaling protein that undergo es autoproteolytic cleavage to generate amino- and carboxy-terminal pr oducts. We have found that both floor plate cells and motor neurons ar e induced by the aminoterminal cleavage product of SHH (SHH-N). the th reshold concentration of SHH-N required for motor neuron induction is about 5-fold lower than that required for floor plate induction. Highe r concentrations of SHH-N can induce floor plate cells at the expense of motor neuron differentiation. Our results suggest that the inductio n of floor plate cells and motor neurons by the notochord In vivo is m ediated by exposure of neural plate cells to different concentrations of the aminoterminal product of SHH autoproteolytic cleavage.