B6J.Cg-Tg(Mnx1-cre/ERT2)8Rbro/Mmjax

Stock number: 037087
Product name: Hb9::CreER^T2
Research areas: Neurobiology Research, Research Tools

Description

Hb9::CreER^T2 transgenic mice express a tamoxifen inducible Cre recombinase/ERT2 fusion under the control of the mouse Mnx1 (also known as Hb9) promoter elements. Cre recombinase activity is observed specifically in Hb9-expressing interneurons. This strain may be useful in studies of neural circuits.

Detailed description

Mnx1 (motor neuron and pancreas homeobox 1, also known as Hb9) encodes a transcription factor that contains a homeobox domain. It is expressed in spinal visceral motor neurons, somatic motor neurons and in a subset of spinal neurons (ventromedial upper lumbar spinal cord) called interneurons (glutaminergic Hb9 interneurons).

Hb9::CreER^T2 transgenic mice contain a mouse Mnx1 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 Mnx1-expressing cells in the offspring. Hemizygous mice are viable and fertile with no reported phenotypic abnormalities. Homozygote viability has not been assessed.

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 bacterial artificial chromosome, RP24-351I23, containing the mouse Mnx1 gene was modified by recombineering to replace the Mnx1 coding region with an inducible Cre recombinase/ERT2 cassette (CreERTT2-BGH poly) and an FRT flanked zeomycin cassette. The zeomycin cassette is retained in the construct but lacks a eukaryotic promoter. The donating investigator has indicated that the BAC only expresses Mnx1. The BAC was microinjected into the pronuclei of fertilized hybrid C57BL/6 x CBA oocytes. The transgene insertion site is unknown. All founder lines were confirmed for tamoxifen induce recombination in motor neurons between E11-E14. Founder line 8 was bred to C57BL/6J mice. Mice were backcrossed to C57BL/6J for at least 11 generations. Upon arrival at The Jackson Laboratory in 2025, sperm was cryopreserved. To establish our live colony, an aliquot of frozen sperm was used to fertilize C57BL/6J oocytes (Stock No. 000664).

In 2025, expanded quality control screening at The Jackson Laboratory revealed that the Hb9::CreER^T2 transgenic mice we received were all lacZ positive. Furthermore, after three additional generations of backcrossing to C57BL/6J, all the Hb9::CreER^T2 transgenic mice were lacZ positive (n=27), while all non-transgenic littermates were lacZ negative (n=23). This strongly suggests the Hb9::CreER^T2 transgene contains a lacZ sequence. It has not been determined if the lacZ has any effect on Hb9::CreER^T2 expression or if the lacZ is useful for staining purposes.

Allele

Symbol: Tg(Mnx1-cre/ERT2)8Rbro
Name: transgene insertion 8, Robert M Brownstone
MGI accession ID: MGI:6758656
Generation method: Transgenic
Attributes: Recombinase-expressing; Inducible
Synonyms: Hb9::CreER^T2
Marker symbol: Tg(Mnx1-cre/ERT2)8Rbro
Marker name: transgene insertion 8, Robert M Brownstone
Chromosome: UN
Strain of origin: C57BL/6 x CBA
Molecular note: The bacterial artificial chromosome (BAC) clone RP24-351I23 containing the mouse Mnx1 (Hb9) gene was modified using recombineering bacterial strain to introduce the cre/ERT2-BGH polyA and Frt-Zeo-Frt selection cassette into the exon 1 replacing the Mnx1 coding region. The Frt-Zeo-Frt cassette is retained in the transgene but lacks a eukaryotic promoter. Three founder lines (4, 8, and 10) were generated. Line 10 gave low-level inducible activity and was terminated. Line 4 and Line 8 displayed similar inducible recombination activity in the desired cell populations and were maintained. Lines 4 and 8 were indistinguishable, and line 8 was used for the majority of studies described. Unpublished results indicated that this allele is likely to include a lacZ sequence; however, its expression/function is unknown.