Full-length cDNA cloning and distribution of human dopamine D4 receptor

Dopamine D4 receptor is the focus of interest in terms of pharmacological profile and possible relation to the disease. Using poly A + RNA from human retina as a template, we succeeded in cloning of full-length cDNA of the human dopamine D4 receptor by improved reverse transcription-polymerase chain reaction (RT-PCR). From the RT-PCR products, two polymorphic variants which had two and four tandem repeats in the putative third cytoplasmic loop were obtained. Transient expression of the full-length cDNA in COS-I cells produced [3H]spiperone binding sites with a high affinity. These results confirmed the existence of the D4 receptor mRNA containing a different number of polymorphic tandem repeats in native human tissues. The RT-PCR method demonstrated the restricted distribution of the D4 mRNA in human tissues and brain regions. The mRNA was detected at the highest level in the retina, followed by the brain, placenta, and kidney. Among brain regions, relatively low levels for mRNA of the human D4 receptor were observed in the nigrostriatal pathway compared with the mesolimbic system. The distribution of the mRNA in human brain suggests that the D4 receptor plays a different role in the central nervous system compared with the D2 receptor.