B6(Cg)-B2m^{tm1c(EUCOMM)Hmgu}/J

Stock number: 034858
Product name: B2m^fl/fl
Research areas: Cancer Research, Immunology, Inflammation and Autoimmunity Research, Research Tools

Description

B2m^fl/fl mice have loxP sites flanking exons 2-4 of the beta-2 microglobulin gene (B2m). Exposure to Cre recombinase removes the floxed sequence - creating a null allele and preventing the expression of MHC class I protein in cells as directed by the cre promoter. These B2m^fl/fl mice may be useful in studying immunology, oncology, or infectious disease.

Detailed description

The beta-2 microglobulin (B2m) gene encodes the MHC class I antigen which functions as a "self-recognition" marker on the cell surface. The B2m^fl allele has loxP sites flanking exons 2-4 of the beta-2 microglobulin gene. Exposure to Cre recombinase removes the floxed sequence - creating a null allele. Prior to introduction of Cre recombinase, mice heterozygous or homozygous for the B2m^fl allele are viable and fertile with normal breeding, and have no gross physical or behavioral abnormalities.

When B2m^fl mice are bred to mice that express Cre recombinase, the resulting offspring will have exons 2-4 deleted - creating a null allele in the cells/tissues as determined by the cre promoter. For example, when crossed to a tamoxifen inducible global R26-CreERT2 (Stock No. 008463) or a T cell-specific CD4-CreER^T2 (Stock No. 022356), the resulting progeny can be used to examine NK cell "missing-self" reactivity (Bern et al. 2018).

Development

The B2m^fl floxed allele was created in the laboratory of Dr. Wayne M. Yokoyama (Washington University School of Medicine). First, a targeting vector was designed to insert an FRT site followed by lacZ sequence and a loxP site, beginning at position 122150436 (GRCm38), upstream of exon 2 of the beta-2 microglobulin gene (B2m) on Chromosome 2. This first loxP site was followed by a neomycin resistance gene under the control of the human beta-actin promoter, SV40 polyA, a second FRT site and a second loxP site. A third loxP site was inserted downstream of the targeted exon(s) at position 122153310, downstream of exon 4. The construct was electroporated into C57BL/6N-A^tm1Brd-derived JM8A3.N1 ES cells. Correctly targeted cells were then injected into recipient blastocyts and chimeric mice were bred with albino C57BL/6J (Stock No. 000058) mice for germline transmission. Progeny containing the B2m^{tm1a(EUCOMM)Hmgu} allele were then crossed to FLPe-expressing C57BL/6-Tg(CAGGS-Flpe)2Arte mice to remove the neo and lacZ cassettes, creating the conditional (floxed) B2m^{tm1c(EUCOMM)Hmgu} allele.

In 2020, males were sent to The Jackson Laboratory. 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).

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. Four of the 5 markers that determine C57BL/6J from C57BL/6N were found to be segregating. These data suggest the mice sent to The Jackson Laboratory Repository were on a mixed C57BL/6N;C57BL/6J genetic background.

Allele

Symbol: B2m^{tm1c(EUCOMM)Hmgu}
Name: targeted mutation 1c, Helmholtz Zentrum Muenchen GmbH
MGI accession ID: MGI:6369398
Generation method: Targeted
Attributes: Conditional ready (e.g. floxed)
Synonyms: B2m^fl
Marker symbol: B2m
Marker name: beta-2 microglobulin
Marker synonyms: AMYLD6; beta 2 microglobulin; beta2-m; IMD43; Ly-m11; MHC1D4
Chromosome: 2
Strain of origin: C57BL/6N-A^tm1Brd
Molecular note: The L1L2_Bact_P cassette was inserted at position 121980917 of Chromosome 2 upstream of the critical exon(s) (Build GRCm39). The cassette is composed of an FRT site followed by lacZ sequence and a loxP site. This first loxP site is followed by a neomycin resistance gene under the control of the human beta-actin promoter, SV40 polyA, a second FRT site and a second loxP site. A third loxP site is inserted downstream of the targeted exon(s) at position 121983791. The critical exon(s) is/are thus flanked by loxP sites. A "conditional ready" (floxed) allele was created by flp recombinase expression in mice carrying this allele to remove the lacZ sequence and neo selection cassette, leaving loxP sites flanking the critical exon(s). Further information on targeting strategies used for this and other IKMC alleles can be found at http://www.informatics.jax.org/mgihome/nomen/IKMC_schematics.shtml