MOTOR NEURON-DERIVED RETINOID SIGNALING SPECIFIES THE SUBTYPE IDENTITY OF SPINAL MOTOR-NEURONS

The diversification of neuronal cell types in the vertebrate central n ervous system depends on inductive signals provided by local organizin g cell groups of both neural and nonneural origin. The influence of si gnals provided by postmitotic neurons on the fate of neurons born at s ubsequent development stages, however, remains unclear. We provide evi dence that a retinoid-mediated signal provided by one subset of early- born spinal motor neurons imposes a local variation in the number of m otor neurons generated at different axial levels and also specifies th e identity of a later-born subset of motor neurons. Thus, in the verte brate central nervous system the distinct fates of late-born neurons m ay be acquired in response to signals provided by early-born neurons.