Characterization of the rat A2A adenosine receptor gene:: a 4.8-kb promoter-proximal DNA fragment confers selective expression in the central nervous system

We isolated and characterized a 4.8-kb 5' flanking region of the rat A(2A) adenosine receptor (A(2A)-R) gene in the present study. Promoter activity was observed with this DNA fragment in PC12 cells and C6 cells which contain endogenous A(2A)-Rs. A fusion fragment consisting of the 4.8-kb promoter-proximal DNA fragment of the A(2A)-R gene, and the coding region of lacZ was utilized to produce mice harbouring the fusion gene. In three independent founder lines, proteins and transcripts of the transgene were found in many areas of the central nervous system (CNS), but not in three peripheral tissues examined. Double immunohistochemical analyses revealed that the transgene was coexpressed with endogenous A(2A)-R and proper neuronal markers in the brain. Specifically, the transgene in the striatum was found in the enkephalin-containing GABAergic neurons and in the cholinergic neurons as was found for the endogenous A(2A)-R. However, a selectively enriched striatal expression of the transgene was not found as was observed for the endogenous A(2A)-R. Collectively, the 4.8-kb promoter-proximal DNA fragment of the rat A(2A)-R gene contains important element(s) to direct its expression in the CNS where functional A(2A)-R are found, but were not sufficient to confer the highly concentrated expression of the striatal A(2A)-R. Furthermore, expressions of A(2A)-R and the transgene were found in both neurons and astrocytes, suggesting that adenosine might mediate its function through A(2A)-R in both cell types.