Isolating and characterizing three alternatively spliced mu opioid receptor variants: mMOR-1A, mMOR-1O, and mMOR-1P

Area of Science:

• Neuroscience
• Molecular Biology
• Genetics

Background:

• Alternative pre-mRNA splicing of the mu opioid receptor gene (OPRM1) generates diverse variants in mammals.
• Three main classes of OPRM1 splice variants exist: full-length, 6TM, and single TM variants.

Purpose of the Study:

• To isolate and characterize three novel full-length C-terminal splice variants of the mouse OPRM1 gene: mMOR-1A, mMOR-1O, and mMOR-1P.
• To investigate the regional expression patterns and functional properties of these new variants.

Main Methods:

• Reverse transcription quantitative PCR (RT-qPCR) was used to assess mRNA expression levels in different brain regions.
• Functional characterization involved expressing variants in Chinese Hamster Ovary cells and performing binding affinity assays and [³⁵S]γGTP binding assays.

Main Results:

• Three new full-length mouse OPRM1 splice variants (mMOR-1A, mMOR-1O, mMOR-1P) were identified.
• Differential mRNA expression of these variants was observed across brain regions, indicating region-specific splicing.
• All variants exhibited high mu-opioid receptor binding affinity and selectivity, with variations in agonist affinities and G protein activation potency and efficacy.

Conclusions:

• The identified OPRM1 variants display distinct functional properties, contributing to the complexity of mu-opioid receptor signaling.
• Evidence supports biased signaling, where different agonists activate signaling pathways differently within and among OPRM1 variants.
• These findings underscore the importance of OPRM1 splice variants in mediating region-specific opioid responses.