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Characterization of the murine mu opioid receptor gene
D L Kaufman1, D E Keith, B Anton
1Department of Molecular and Medical Pharmacology, University of California, Los Angeles 90024, USA.
Abstract:
The analgesic and addictive properties of morphine and other opioid drugs are thought to result from their interaction with mu opioid receptors. Using a delta opioid receptor cDNA as a probe, we have isolated a murine mu opioid receptor cDNA clone (mMOR). Stable expression of mMOR in Chinese hamster ovary cells conferred high binding affinity for mu receptor ligands including morphine and [D-Ala2,N-methyl-Phe4,Gly5-ol]-enkephalin and low affinity for delta and kappa preferring ligands. Treatment of these cell lines with morphine and other mu agonists inhibited forskolin-induced cAMP accumulation, demonstrating a functional coupling of mMOR to the inhibition of adenylate cyclase. The predicted amino acid sequence of mMOR shares approximately 55% overall amino acid identity with the delta receptor and approximately 97% identity with the recently reported rat mu opioid receptor. Expression of the mu receptor in mouse brain as revealed by in situ hybridization parallels the reported pattern of distribution of mu-selective ligand binding sites. Chromosomal localization (to mouse chromosome 10) and Southern analysis are consistent with a single mu opioid receptor gene in the mouse genome, suggesting that the various pharmacologically distinct forms of the mu receptor arise from alternative splicing, post-translational events, or from a highly divergent gene(s).
Insights
Researchers identified the mouse mu opioid receptor (mMOR) gene, crucial for morphine
Area of Science:
- Neuroscience
- Molecular Biology
- Pharmacology
Background:
- Opioid drugs, like morphine, exert analgesic and addictive effects through mu opioid receptors.
- Understanding the molecular basis of mu opioid receptor function is key to developing safer analgesics.
Purpose of the Study:
- To isolate and characterize the murine mu opioid receptor (mMOR) cDNA.
- To investigate the functional properties and gene structure of the mouse mu opioid receptor.
Main Methods:
- Used a delta opioid receptor cDNA probe to isolate the mMOR cDNA clone.
- Expressed mMOR in Chinese hamster ovary cells for binding and functional assays.
- Analyzed mMOR amino acid sequence, expression in mouse brain (in situ hybridization), and chromosomal localization.
Main Results:
- Stable expression of mMOR conferred high affinity for mu-selective ligands and inhibited adenylate cyclase.
- mMOR shares high sequence identity with the rat mu opioid receptor and shows specific expression patterns in the mouse brain.
- Evidence suggests a single mMOR gene in mice, with receptor diversity potentially arising from alternative splicing or post-translational modifications.
Conclusions:
- The isolated mMOR clone represents a functional mu opioid receptor.
- The findings provide insights into the molecular mechanisms underlying opioid drug action and receptor diversity.