C57BL/6-Oprm1^{tm2.1(EGFP/cre)Ics}/KffJ

Stock number: 038053
Product name: Oprm1-cre
Research areas: Neurobiology Research, Research Tools

Description

Oprm1-cre knock-in mice express an eGFP/Cre fusion protein in opioid receptor, mu 1-expressing cells while retaining endogenous Oprm1 activity. These mice may be used for studying the expression and activity pattern of Oprm1-expressing cells.

Detailed description

The Oprm1 gene codes for the mu 1 opioid receptor (MOR), which couples with G proteins in the central nervous system and is involved with regulation of multiple physiological functions, but primarily nociception. Consistent stimulation of MORs with endogenous or exogenous opioids, may lead to drug tolerance, dependence and ultimately addiction. This Oprm1-cre knock-in strain has an eGFP/Cre fusion protein sequence inserted into exon 4 of the Oprm1 gene, in frame and 5’ of the stop codon. Endogenous Oprm1 expression and function are fully retained in this knock-in model.

Homozygous Oprm1-cre knock-in mice are viable and fertile with no reported overt phenotype. When Oprm1-cre knock-in mice are bred with mice containing lox-flanked sequences, Cre-mediated recombination will result in deletion of the floxed sequences in Oprm1-expressing cells in the offspring.

When bred to Rosa^lsltdTomato reporter mice, removal of the floxed STOP cassette results in tdTomato expression in Oprm1-cre-expressing cells of the offspring. The resulting cre-expressing offspring demonstrated high tdTomato expression in the basal ganglia, thalamus, the entire mesolimbic and medial habenula-interpeduncular nucleus pathways and most of the amygdala. The donating laboratory did not examine cre expression in tissues other than brain. This strain may be useful for mapping the expression pattern, and evaluating the function, of Oprm1 in pain, reward and addiction research.

Of note, the donating investigator has indicated that the level of GFP is too low to detect by direct fluorescence but is detectable utilizing anti-GFP antibodies or in situ hybridization.

Development

The Oprm1-cre knock-in targeting vector was designed to insert a T2A-EGFP/Cre fusion protein sequence in exon 4, in-frame immediately upstream of the termination codon, of the opioid receptor, mu 1 (Oprm1) gene followed by an FRT-flanked neomycin selection cassette. The construct was electroporated into C57BL/6N-derived S3 embryonic stem (ES) cells (PHENOMIN-ICS). Correctly targeted ES cells were injected into blastocysts and the resulting chimeric mice were identified by genotyping and bred to C57BL/6NTac-Gt(ROSA)26Sor^{tm2(CAG-flpo,-EYFP)Ics}/Ics (InfraFrontier EMMA ID EM:05490) to remove the neo cassette. The FlpO transgene was removed through selective breeding to C57BL/6NCrl mice. The resulting Oprm1-cre heterozygous mice were maintained on a C57BL/6NCrl background by the donating laboratory (see SNP notes below). Upon arrival at The Jackson Laboratory in 2023, sperm was cryopreserved. To establish our live colony, an aliquot of frozen sperm was used to fertilize C57BL/6NJ oocytes (Stock No. 005304).

In 2023, a 48 SNP (single nucleotide polymorphism) panel analysis, with 43 markers covering all 19 chromosomes and the X chromosome, as well as 5 markers that distinguish between the C57BL/6J and C57BL/6N substrains, was performed on the males sent to The Jackson Laboratory Repository (and cryopreserved). While the 43 markers throughout the genome suggested a C57BL/6 genetic background, 5 of 5 markers that determine C57BL/6J from C57BL/6N were found to be segregating in those mice. These data suggest that the mice sent to The Jackson Laboratory Repository were on a mixed C57BL/6 genetic background.

Allele

Symbol: Oprm1^{tm2.1(EGFP/cre)Ics}
Name: targeted mutation 2.1, Mouse Clinical Institute
MGI accession ID: MGI:6755589
Generation method: Targeted
Attributes: Recombinase-expressing; Reporter; No functional change
Synonyms: Oprm1^{tm5.1(EGFP/cre)Kff}; Oprm1-Cre
Marker symbol: Oprm1
Marker name: opioid receptor, mu 1
Marker synonyms: LMOR; MOP; MOP receptor; MOP-R; mor; MOR1; M-OR-1; MOR-1; MORA; muOR; Oprm; Oprrm1
Chromosome: 10
Strain of origin: C57BL/6N
Molecular note: A targeting vector was designed to insert a T2A-EGFP/Cre fusion protein in exon 4 in frame just upstream of the stop codon, of the opioid receptor, mu 1 (Oprm1) coding region. Flp-mediated recombination removed the FRT-flanked neo cassette.