B6(Cg)-Tg(Acta2-cre/ERT2)1Ikal/J

Stock number: 032758
Product name: alphaSMACreERT2
Research areas: Internal/Organ Research, Research Tools

Description

αSMACreERT2 transgenic mice express a tamoxifen inducible Cre recombinase/ERT2 fusion under the control of the mouse Acta2 (actin alpha 2, smooth muscle, aorta or αSMA) promoter. Cre recombinase activity is observed in smooth muscle cells (e.g., blood vessels, lung airways, gut and bladder) as well as a population of mesenchymal progenitor cells. This strain may be useful in lineage tracing studies of bone remodeling and regeneration.

Detailed description

Acta2 (actin alpha 2, smooth muscle, aorta or αSMA) encodes a smooth muscle actin expressed in a population of mesenchymal progenitor cells located in perivascular niches, the periosteum and sutures. This population of cells plays a role in bone remodeling and regeneration. αSMACreERT2 transgenic mice contain a mouse Acta2 promoter directing tamoxifen-inducible Cre recombinase expression. When transgenic mice are bred with mice containing loxP-flanked (floxed) sequences, tamoxifen-inducible cre-mediated recombination will result in deletion of floxed sequences in αSMA-expressing cells in the offspring. Hemizygous and homozygous mice are viable and fertile with no reported phenotype abnormalities.

Double mutant αSMACreERT2 and Gt(ROSA)26Sor^{tm9(CAG-tdTomato)Hze} (Ai9; Stock No. 007909) mice administered tamoxifen have SMA9+ cells detected in the primary spongiosa or the periosteum, but not within the bone matrix. No leaky expression of tdTomato is detected in bone tissue, however, cre expression is observed in tissues with strong αSMA expression like bladder and aorta. 17 days following tamoxifen administration tdTomato labeling identifies multiple osteoblasts and osteocytes. This strain may be useful in lineage tracing studies of bone remodeling and regeneration. Outside of bone tdTomato expression is observed in perivascular cells within various tissues (skin, liver, kidney, lungs) and in myoepithelial cells with progenitor characteristics within the mammary glands and olfactory glands.

The Cre-ERT2 fusion protein consists of Cre recombinase fused to a triple mutant form of the human estrogen receptor which does not bind its natural ligand (17β-estradiol) at physiological concentrations but will bind the synthetic estrogen receptor ligands 4-hydroxytamoxifen (OHT or tamoxifen) and, with lesser sensitivity, ICI 182780. Restricted to the cytoplasm, Cre-ERT2 can only gain access to the nuclear compartment after exposure to tamoxifen. To counteract the mixed estrogen agonist effects of tamoxifen injections, which can result in late fetal abortions in pregnant mice, progesterone may be coadministered.

Development

The αSMACreERT2 transgenic construct contains the mouse Acta2 promoter (1.1 kb) directing expression of cre/ERT2. creERT2 is inserted downstream of intron 1 and followed by GH-polyA sequence. The construct was microinjected into the pronuclei of fertilized C57BL/6 oocytes. Founder line 1 was established. The transgene insertion site is unknown. Upon arrival, sperm was cryopreserved. To establish our live colony, an aliquot of frozen sperm was used to fertilize C57BL/6J oocytes (Stock No. 000664).

Allele

Symbol: Tg(Acta2-cre/ERT2)1Ikal
Name: transgene insertion 1, Ivo Kalajzic
MGI accession ID: MGI:5461154
Generation method: Transgenic
Attributes: Recombinase-expressing; Inducible
Synonyms: alphaSMACreERT2
Marker symbol: Tg(Acta2-cre/ERT2)1Ikal
Marker name: transgene insertion 1, Ivo Kalajzic
Chromosome: UN
Strain of origin: C57BL/6
Molecular note: The cre/ERT2 cDNA and BGH polyA cDNAs was inserted into a construct containing the vascular smooth muscle alpha-actin (Acta2) promoter. Functionality of the construct to modify floxed reporter constructs was tested by transient transfection of smooth muscle cell cultures. The purified vector was injected into fertilized C57BL/6 oocytes.