BMP growth factors and Phox2 transcription factors can induce synaptotagmin I and neurexin I during sympathetic neuron development

Synaptotagmin I and neurexin I mRNAs, coding for proteins involved in neuro transmitter secretion, become detectable in primary sympathetic ganglia sho rtly after initial induction of the noradrenergic transmitter phenotype. To test whether the induction of these more general neuronal genes is mediate d by signals known to initiate noradrenergic differentiation in a neuronal subpopulation, we examined their expression in noradrenergic neurons induce d by ectopic overexpression of growth and transcription factors. Overexpres sion of BMP4 or Phox2a in vivo results in synaptotagmin I and neurexin I ex pression in ectopically located noradrenergic cells. In vitro, BMP4 initiat es synaptotagmin I and neurexin I expression in addition to tyrosine hydrox ylase induction. Thus, the induction of synaptotagmin I and neurexin I, whi ch are expressed in a large number of different neuron populations, can be accomplished by growth and transcription factors available only to a subset of neurons. These findings suggest that the initial expression of proteins involved in neurotransmitter secretion is regulated by different signals i n different neuron populations. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.