Structural and functional characterization of mouse glutamate decarboxylase 67 gene promoter

Neuronal expression of the mouse glutamate decarboxylase 67 (mGAD67) gene occurs exclusively in neurons that synthesize and release GABA (GABAergic neurons). This gene is also expressed in pancreatic islet cells and testicular spermatocytes. In order to elucidate the molecular mechanisms underlying the regulation of mGAD67 gene expression, we isolated and characterized the 5'-flanking region of this gene. Sequence analysis of a 10.2-kb DNA fragment of this gene containing a promoter region (8.4 kb) and noncoding exons 0A and 0B revealed the presence of numerous potential neuron-specific cis-regulatory elements. Functional analysis of the 5'-flanking region of exons 0A and 0B by transient transfection into cultured cells revealed that the region -98 to -52 close to exon 0A is important for the transcriptional activity of both exons 0A and 0B. In addition, we used transgenic mice to examine the expression pattern conferred by the 10.2 kb DNA fragment of the mGAD67 gene fused to the bacterial lacZ reporter gene. Transgene expression was observed in neurons of particular brain regions containing abundant GABAergic neurons such as the basal ganglia, in pancreatic islet cells and in testicular spermatocytes and spermatogonia. These results suggest that the 10.2 kb DNA fragment of the mGAD67 gene contains regulatory elements essential for its targeted expression in GABAergic neurons, islet cells and spermatocytes.