B6(Cg)-Calb2^tm1(cre)Zjh/J

Stock number: 010774
Product name: Cr-iCre
Research areas: Neurobiology Research, Research Tools

Description

Cr-IRES-Cre (Calb2-IRES-Cre) mice have Cre recombinase expression directed to calretinin interneurons in the brain and cortex by the endogenous promoter/enhancer elements of the Calb2 locus (calbindin 2; also called calretinin or CR).

Detailed description

The Cr-IRES-Cre (Calb2-IRES-Cre) allele harbors an internal ribosome entry site and Cre recombinase in the 3' UTR of the Calb2 locus (calbindin 2; also called calretinin or CR). As such, it is designed to have the endogenous Calb2 promoter/enhancer elements directing cre expression to calretinin interneurons in the brain and cortex. When Calb2-IRES-Cre mice are bred with mice containing loxP-flanked sequences, Cre-mediated recombination will result in deletion of the floxed sequences in the Calb2-expressing cells of the offspring. Calb2 expression from the Calb2-IRES-Cre allele has not been evaluated. Additional phenotype information described below.

In 2009, the donating investigator reported that Cre recombinase activity is specific and efficient (largely recapitulates the endogenous Calb2 expression pattern with highly efficient recombination). They did not examine cre expression in tissues other than brain. Calb2 expression from the Calb2-IRES-Cre allele was not evaluated. They also reported that homozygous mice are viable, fertile, normal in size and do not display any gross physical or behavioral abnormalities.

For characterization information, see images at the Allen Institute for Brain Science website (Calb2-IRES-Cre images).

If the recombinase activity pattern of this allele is further characterized by the Genetic Resource Science group at The Jackson Laboratory, such findings will be reported on the Mouse Genome Informatics (MGI) Allele Detail entry (Calb2^tm1(cre)Zjh). This same information would also be found searching the MGI Recombinase Activity database.

Development

A targeting vector was designed to insert an internal ribosome entry site (IRES), a Cre recombinase sequence, an SV40 polyA signal, and an frt-flanked neo cassette into the 3' untranslated region (~60 bp after the translational termination site) of the Calb2 gene (calbindin 2; also called calretinin or CR). This construct was electroporated into C57BL/6-derived Bruce4 embryonic stem (ES) cells. Correctly targeted ES cells were injected into recipient blastocysts and chimeric mice were bred with white C57BL/6 mice to originate the colony. Mutant mice were bred with Actin-FLPe mice (on a C57BL/6 congenic background (N10); see Stock No. 005703) to remove the neo selection cassette. These Cr-IRES-Cre (Calb2-IRES-Cre) mice were subsequently bred with wildtype C57BL/6 (see SNP notes below) mice for approximately three generations (and the FLPe transgene was removed) prior to arrival at The Jackson Laboratory. Upon arrival, mice were bred with C57BL/6J inbred mice (Stock No. 000664) for at least one generation to establish the Cr-IRES-Cre colony.

In 2021, 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 rederived living colony at The Jackson Laboratory Repository. While the 43 markers throughout the genome suggested a C57BL/6 genetic background, one of the 5 markers that determine C57BL/6J from C57BL/6N was found to be segregating. This marker was the rd8 recessive mutation associated with retinal degeneration on Chromosome 1 within the Crb1 locus. These data suggest the mice sent to The Jackson Laboratory Repository were on a mixed C57BL/6N;C57BL/6J genetic background.

Allele

Symbol: Calb2^tm1(cre)Zjh
Name: targeted mutation 1, Z Josh Huang
MGI accession ID: MGI:4365736
Generation method: Targeted
Attributes: Recombinase-expressing
Marker symbol: Calb2
Marker name: calbindin 2
Chromosome: 8
Strain of origin: C57BL/6
Expressed genes: cre,cre recombinase,bacteriophage P1
Site of expression: cre expression is directed to calretinin interneurons in the brain and cortex by the endogenous Calb2 promoter/enhancer elements.
Molecular note: A targeting vector was designed to insert an internal ribosome entry site (IRES), a Cre recombinase sequence, an SV40 polyA signal, and an frt-flanked neo cassette into the 3' untranslated region (~60 bp after the translational termination site) of the Calb2 (calbindin 2; also called calretinin or CR) gene. Mutant mice were bred with Actin-FLPe mice (on a C57BL/6 congenic background) to remove the neo selection cassette and the transgene was subsequently bred out of the background.