TEMPORAL ONSET OF SYNAPSIN-I GENE-EXPRESSION COINCIDES WITH NEURONAL DIFFERENTIATION DURING THE DEVELOPMENT OF THE NERVOUS-SYSTEM

Synapsin I is the best characterized member of a family of nerve termi nal-specific phosphoproteins implicated in the regulation of neurotran smitter release. During development, the expression of synapsin I corr elates temporally and topographically with synapse formation, and rece nt physiological studies (Lu et al. [1992] Neuron 8:521-529.) have sug gested that synapsin I may participate in the functional maturation of synapses. To better understand the temporal relationship between syna psin I gene expression and particular cellular events during neuronal development, we have used in situ hybridization histochemistry to loca lize synapsin I mRNA throughout the rat central and peripheral nervous systems during embryonic and postnatal development. From the earliest embryonic time points assayed (E12), the expression of the synapsin I gene was detectable in both the central and peripheral nervous system s. While, in general, levels of synapsin I mRNAs were high in utero, s ynapsin I cDNA probes revealed specific patterns of hybridization in d ifferent regions of the embryonic nervous system. To determine precise ly the temporal onset of expression of the synapsin I gene during neur onal development, we examined in detail the appearance of synapsin I m RNA during the well characterized postnatal development of granule cel ls of the rat cerebellum and hippocampus. In both regions, the onset o f synapsin I gene expression correlated with the period of stem cell c ommitment to terminal differentiation. Finally, our data demonstrate t hat, in a second phase, synapsin I gene expression increases to a maxi mum for a given neuronal population during a particular phase of diffe rentiation, i.e., synaptogenesis. (C) 1994 Wiley-Liss, Inc.