We investigated the neuron-specific enolase (NSE) promoter in terms of its promoter strength and neuronal specificity in the cerebellum in vivo. The 1.8 kb rat NSE promoter was divided into three regions, A (0.8 kb), B (0.7 kb), and C (0.3 kb), starting from the 5' side. Then, we made various deletion constructs and assessed them by virally expressing GFP under the control of one of the deleted promoters. Removing region A reduced GFP expression to ~6% of that of the original 1.8 kb promoter. Further deletion of region B (presence of region C alone) did not influence the promoter strength, but removing region B from the original 1.8 kb promoter reduced the GFP expression to ~6% of the original level, similar to the level observed after deletion of region A. Immunohistochemistry showed robust GFP expression in Purkinje cells and modest expression in interneurons by the original promoter. Removing region A and/or region B abolished the GFP expression in Purkinje cells in most cerebellar lobules, with the expression in interneurons almost unchanged. These results suggest that region C, which is a proximal 0.3 kb sequence, contains cis-acting elements that drive transcription predominantly in interneurons. The addition of either region A or B onto region C does not alter the promoter properties; however, the addition of both regions A and B to region C drastically enhanced the promoter activity in Purkinje cells, suggesting the synergistic action of cis-acting regulatory elements in regions A and B for strong activation in Purkinje cells.
Keywords: AAV vector; Interneuron; Neuron-specific enolase; Promoter; Purkinje cell; Viral vector.