B6.FVB(Cg)-Tp(X)1Soff^{Tg(Myh11-icre/ERT2)1Soff}/ZjngJ

Stock number: 036935
Product name: X-linked Myh11-iCreER^T2
Strain synonyms: SMMHC-iCreER^T2
Research areas: Research Tools

Description

SMMHC-CreER^T2 transgenic mice allow sufficient Myh11-driven tamoxifen-inducible Cre expression in smooth muscle cells (SMCs).

Of note, Stock No. 036935 has the SMMHC-CreER^T2 BAC transgene inserted on the X chromosome, whereas Stock No. 019079 contains the same transgene inserted on the Y chromosome. Additionally, Stock No. 037658 has a similar transgene (Myh11-CreER^T2-RAD) integrated into mouse Chromosome 2 in a region devoid of other genes.

Detailed description

Homozygous female and hemizygous male SMMHC-CreERT2 transgenic mice are viable and fertile, with expression of icre/ERT2 under control of the mouse smooth muscle myosin, heavy polypeptide 11, smooth muscle (Myh11) promoter/enhancer regions on the BAC transgene. The donating investigator reports that the BAC transgene inserted on the X Chromosome. Myh11, also known as SMMHC, is a contractile protein expressed only in smooth muscle cells. When female or male SMMHC-CreERT2 mice are bred with mice containing loxP-flanked sequence, tamoxifen-inducible, cre-mediated recombination will result in deletion of the floxed sequences in the smooth muscle cells (SMCs) of the offspring.

Cre-driven recombination in the hemizygous X/X^Cre+ female mice is reduced to half of that observed in hemizygous male Y/X^Cre+ mice and X/Y^Cre+ mice (Stock No. 019079) due to mosaic Cre expression from random X-chromosome inactivation. Homozygous female X^Cre+/X^Cre+ mice produce uniform Cre activity in arterial SMCs.

Of note, Stock No. 019079 and Stock No. 037658 each contain a similar transgene inserted on the Y chromosome and Chromosome 2, respectively.

Development

A bacterial artificial chromosome (BAC) containing the mouse smooth muscle myosin, heavy polypeptide 11, smooth muscle (Myh11) gene was obtained. An icre/ERT2 sequence (a codon improved mutated human estrogen receptor ligand binding domain fused to Cre), a polyadenylation signal, and a frt-flanked beta-lactamase cassette were inserted into the initiation codon of Myh11. After Flp-mediated removal of the beta-lactamase cassette, the modified 180 kb BAC transgene was microinjected into the pronuclei of fertilized FVB/N oocytes. Transgenic mice, in which the transgene integrated on the Y Chromosome, were identified and bred to C57BL/6 mice for at least 8 generations to establish a colony. Some of these mice were sent to The Jackson Laboratory by Dr. Stefan Offermanns (University of Heidelberg) as Stock No. 019079 and some were obtained by Dr. Zhihua Jiang (University of Florida). Dr. Jiang bred male SMMHC-CreERT2 mice to R26R mice (Stock No. 003474) and to Tgfbr1^f/f mice (both on C57BL/6J backgrounds). Through a mechanism of Y to X chromosome translocation, some female carriers acquired the SMMHC-CreERT2 allele. Female SMMHC-CreERT2 mice were bred to C57BL/6J males for at least 5 additional generations, and the R26R and Tgfbr1^f/f alleles were bred out of the colony. Upon arrival at The Jackson Laboratory, sperm was cryopreserved. To establish our live colony, an aliquot of frozen sperm was used to fertilize C57BL/6J oocytes (Stock No. 000664).

In 2021, expanded quality control screening of Stock No. 019079 at The Jackson Laboratory determined the cre/ERT2 sequence to be that of a codon-improved variant icre/ERT2.

Allele

Symbol: Tp(X)1Soff^{Tg(Myh11-icre/ERT2)1Soff}
Name: transgene insertion 1, Stefan Offermanns
MGI accession ID: MGI:6830915
Generation method: Spontaneous
Attributes: Recombinase-expressing
Marker symbol: Tp(X)1Soff
Marker name: transposition, Chr X, Offermanns 1
Chromosome: X
Strain of origin: FVB/N
Molecular note: The mouse promoter from BAC clone 26630 was used to drive inducible icre expression in smooth muscle cells. An FRT-flanked beta-lactamase gene contained within the cre/ESR1 cassette was removed by flp mediated recombination. The transgene that originally integrated into Chr Y was found to to have translocated to Chr X in some female mice in the colony. The exact position is unknown.