The characterisation of the 5′ regulatory region of the D3 dopamine receptor gene

The dopamine D3 receptor gene has been suggested to play a role in neuropsychiatric and neurobehavioural disorders. In vivo studies in rodents indicated upregulation of the D3 receptor gene in limbic areas of the brain after chronic antispsychotic drug treatment. Furthermore, molecular genetics studies have identified a Ball polymorphism in the coding region of the gene to be associated with increased susceptibility to schizophrenia in French and UK populations. In this study, the 5′ flanking region of the rat D3 gene was characterised by isolating the 5′region of cDNA and 4.6 Kb of genomic sequence, which revealed the presence of two new exons 196 bp and 120 bp long, separated by an 855 bp intron, located several kilobases upstream of the previously published six coding exons. The transcription start site was found to localize at a pyrimidine-rich consensus 'initiator' sequence, similar to the rat D2 gene. The D3 promoter lacks TATA or CAAT boxes but unlike that of other dopamine receptor genes has only 52% GC content. Functional analysis of D3 promoter deletion mutants fused to a reporter gene in TE671 cells, which endogenously express this gene, revealed strong transcriptional activity localized within 36 nucleotides upstream of the transcriptional start site, and a potent silencer between bases -37 and -537. The D3 promoter is inactive in C6 and COS-7 cells. We conclude that the D3 gene, similar to the closely related D2 gene, is transcribed from a tissue specific promoter which is under intense negative control.