B6.Cg-Tg(ACTA1-cre/Esr1*)2Kesr/J

Stock number: 031934
Product name: HSA-MCM
Strain synonyms: HSA-MerCreMer
Research areas: Neurobiology Research, Research Tools

Description

HSA-MCM mice express tamoxifen-inducible cre in both limb and craniofacial skeletal muscles.

Similar strains include:
Stock No. 025750 which contains the same promoter driving expression of a MerCreMer tamoxifen inducible Cre recombinase on a STOCK genetic background.
Stock No. 039097 which contains the same promoter driving expression of a Cre-ERT2 fusion protein consisting of Cre recombinase fused to a triple mutant form of the human estrogen receptor.

Detailed description

HSA-MCM mice express MerCreMer double fusion protein under the control of the human ACTA1 (actin, alpha 1, skeletal muscle) promoter. Heterozygous mice are viable and fertile. Homozygotes are also viable but exhibit significantly reduced fertility. Of note, the MerCreMer double fusion protein has substantially greater Cre recombinase activity with less promiscuity compared with the CreMer single fusion protein. When HSA-MCM mice are bred with mice containing loxP-flanked sequences, tamoxifen-inducible Cre-mediated recombination is expected to result in deletion of the floxed sequences in skeletal muscles of the limbs, face/tongue, and diaphragm of the offspring.

The MerCreMer double fusion protein consists of Cre recombinase flanked on each end with a mutated murine estrogen receptor (mer) ligand binding domain (amino acids 281-599, G525R), 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, MerCreMer 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

A transgenic construct was designed to contain a MerCreMer sequence under the control of the human ACTA1 (actin, alpha 1, skeletal muscle) promoter. The MerCreMer double fusion protein has a Cre recombinase cDNA sequence flanked on each end with a mutated murine estrogen receptor (mer) ligand binding domain (amino acids 281-599, G525R), thus rendering cre expression tamoxifen-inducible yet estrogen-insensitive. A β-globin intron II sequence, followed by a polyadenylation sequence, was inserted downstream of the promoter to ensure proper splicing. This HSA-MCM transgene was introduced into (C57BL/6 X C3H)F2 donor oocytes. The donating investigator reports that the resulting offspring from founder line 2 were bred to C57BL/6J mice. 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) and Stock No. 025750 was established. Some of these mice were further backcrossed to C57BL/6J to establish this congenic colony.

Allele

Symbol: Tg(ACTA1-cre/Esr1*)2Kesr
Name: transgene insertion 2, Karyn A Esser
MGI accession ID: MGI:5435875
Generation method: Transgenic
Attributes: Recombinase-expressing; Inducible
Synonyms: HSA-Cre; HSA-MCM; HSA-MerCreMer
Marker symbol: Tg(ACTA1-cre/Esr1*)2Kesr
Marker name: transgene insertion 2, Karyn A Esser
Chromosome: UN
Strain of origin: (C57BL/6 x C3H)F2
Expressed genes: cre/Esr1,Cre recombinase and estrogen receptor 1 fusion gene,
Site of expression: When mice carrying this transgne are bred with mice containing loxP-flanked sequences, tamoxifen-inducible Cre-mediated recombination is expected to result in deletion of the floxed sequences in skeletal muscles of the limbs, face/tongue, and diaphragm of the offspring.
Molecular note: The human alpha-skeletal actin gene promoter (ACTA1; HSA) was cloned into a vector upstream the cre recombinase gene fused at the N- and C-termini to mutated estrogen receptor ligand-binding domains (MerCreMer). A beta-globin intron II sequence followed by a polyadenylation sequence was inserted downstream of the promoter to ensure proper splicing. The construct was injected into B6C3F2 embryos. Five founders were generated and crossed to Rosa-lacz reporter mice to assess germline transmission and inducible muscle-specific recombinase activity. Line 2 was established.