SPINAL-CORD NEURONAL PRECURSORS GENERATE MULTIPLE NEURONAL PHENOTYPESIN CULTURE

Neuronal restricted precursors (NRPs) (Mayer-Proschel et al., 1997) ca n generate multiple neurotransmitter phenotypes during maturation in c ulture. Undifferentiated E-NCAM(1) (embryonic neural cell adhesion mol ecule) immunoreactive NRPs are mitotically active and electrically imm ature, and they express only a subset of neuronal markers. Fully matur e cells are postmitotic, process-bearing cells that are neurofilament- M and synaptophysin immunoreactive, and they synthesize and respond to different subsets of neurotransmitter molecules. Mature neurons that synthesize and respond to glycine, glutamate, GABA, dopamine, and acet ylcholine can be identified by immunocytochemistry, RT-PCR, and calciu m imaging in mass cultures. Individual NRPs also generate heterogeneou s progeny as assessed by neurotransmitter response and synthesis, demo nstrating the multipotent nature of the precursor cells. Differentiati on can be modulated by sonic hedgehog (Shh) and bone morphogenetic pro tein (BMP)-2/4 molecules. Shh acts as a mitogen and inhibits different iation (including cholinergic differentiation). BMP-2 and BMP-4, in co ntrast, inhibit cell division and promote differentiation (including c holinergic differentiation). Thus, a single neuronal precursor cell ca n differentiate into multiple classes of neurons, and this differentia tion can be modulated by environmental signals.