Molecular cloning and characterization of the mouse dopamine D3 receptor gene: an additional intron and an mRNA variant.

The intron-exon organization for the murine dopamine D3 receptor gene was determined. A novel intron of approximately 1 kb was identified in both rat and mouse D3 receptor genes. This intron (termed intron 4) is situated between coding nucleotides 723 and 724, resulting in a split of former exon 4 (containing nucleotides 527-801) into two separate exons (exon 4 and exon 5). Thus, the coding regions of the D2 and D3 receptor genes contain an identical number of exons (seven exons) and share a very similar gene structure. Reverse transcription-PCR experiments revealed a short form of mouse D3 mRNA (D3Short) that lacks the first 63 nucleotides from exon 6, and results from a splicing event occurring within this exon. However, this mRNA variant was not found in either rat or human brain. No dopamine D3 receptor mRNA variants were found deriving from the alternative splicing of exon 5, although its counterpart, exon 6 in the D2 receptor gene, is spliced out to produce the D2Short mRNA. These data suggest that, although the intron-exon organizations of the D2 and D3 receptor genes are similar, the encoded transcripts may be processed differently.