| Abstract: |
The mu opioid receptor plays an important role in mediating the pharmacological actions of morphine and morphine-like drugs, such as heroin. Our previous studies showed that the mouse Oprm gene undergoes extensive splicing, as demonstrated by the identification of 15 exons whose combinations generated at least 16 variants. We also isolated two new variants from the human Oprm gene. In the present studies, we report the identification and characterization of four new splice variants from the rat Oprm gene. Using a 3'-RACE approach, we isolated three new exons, exons 7, 8 and 9, from downstream of exon 3. Sequence analysis indicated that the rat exons 7 and 9 were homologous to the mouse exons 7 and 9, respectively, and the rat exon 8 did not share any homology with any known exons. Northern blot analysis with the new exon probes showed distinctive and abundant transcripts of the variants in brain. Three full length cDNA clones containing the new exons, rMOR-1C1, rMOR-1C2 and rMOR-1C3, were obtained by using an RT-PCR approach. All the variants contained the same exons 1, 2 and 3 as the original rMOR-1, but had a different sequence downstream of exon 3 resulting from combinations of the three new exons. Using an RT-PCR strategy, we also isolated a new variant, rMOR-1A, which was a homolog of hMOR-1A or mMOR-1A previously reported. The pharmacological profiles of the variants were studied in CHO cells stably transfected with the variant cDNAs with opioid binding and 35S-gamma-GTP binding assays. |
