THE 5'-FLANKING REGION OF THE RAT SYNAPSIN-I GENE DIRECTS NEURON-SPECIFIC AND DEVELOPMENTALLY-REGULATED REPORTER GENE-EXPRESSION IN TRANSGENIC MICE

The expression of the synapsin I gene is neuron-specific and developme ntally regulated. As a step toward characterizing the molecular mechan isms that are responsible for its transcriptional regulation in vivo, we have generated transgenic mice that carry the chloramphenicol acety ltransferase (CAT) reporter gene under the control of approximately 4, 300 nucleotides of 5'-flanking sequence of the rat synapsin I gene. In four independent transgenic mouse lines, high level CAT expression is observed specifically in the brain and other neural tissues. Two of t hese lines also exhibit notable CAT expression in testis. The transgen e is expressed at similar levels in many different regions of the cent ral nervous system. Immunohistochemical staining detects the CAT marke r protein in various cell populations of neuronal morphology within th e brain and the spinal cord. Transgene expression is developmentally r egulated in a way that correlates well with the expression of the endo genous synapsin I gene. Both follow a characteristic, biphasic postnat al time course with a maximum around day 20. We conclude that the DNA region investigated contains cis-regulatory elements sufficient to dri ve the expression of a reporter gene in a spatial and temporal pattern that resembles the expression of the endogenous synapsin I gene.