STOCK Trp53^tm1Brd Brca1^tm1Aash Tg(LGB-cre)74Acl/J

Stock number: 012620
Product name: BLG-Cre; Brca1^F22-24; p53 KO
Strain synonyms: BLG-Cre; Brca1^{F22-24/F22-24}; p53+/-
Research areas: Cancer Research, Endocrine Deficiency Research, Neurobiology Research, Research Tools

Description

These mice carry the beta-lactoglobulin Cre (BLG-Cre) transgene, are homozygous for floxed exons 22-24 of the breast cancer 1 (Brca1) allele, and are heterozygous for p53 tumor-suppressor gene (Trp53) deficiency. This strain may be useful for studying human basal-like cancer and breast cancer, as well as providing a useful tool for testing new therapeutics.

Detailed description

BLG-Cre; Brca1^tm1Aash; Trp53^+/- mice that carry the beta-lactoglobulin Cre (BLG-Cre) transgene are homozygous for floxed exons 22-24 of the breast cancer 1 (Brca1) allele, and are heterozygous for p53 tumor-suppressor gene (Trp53) deficiency. Mice of this genotype are viable, fertile, normal in size and do not display any behavioral abnormalities. BLG-Cre; Brca1^tm1Aash; Trp53^+/- females have expression of the BLG-Cre transgene during lactation; which leads to loss of Brca1 function in the mammary gland. This results in formation of mammary tumors exhibiting high grade central necrosis and metaplastic elements in the form of spindle cell and squamous cell differentiation; as seen in human basal-like breast cancers and BRCA1 mutation carriers. Heterozygosity for the mutant p53 allele accelerates the formation of mammary tumors. This strain may be useful for studying human basal-like cancer and breast cancer, as well as providing a useful tool for testing new therapeutics.

Development

This mouse colony harbors three mutations: a p53^- mutation, the Brca1^F22-24 mutation, and a BLG-Cre transgene. The description of each is below.

To generate the p53 mutant allele, a targeting vector was designed to replace part of exon 5 of the mouse p53 tumor-suppressor gene, p53, with a PolII-neomycin (neo) resistance cassette (Harvey et al, Nat Gen, 1993; 5; 225-29). This construct was electroporated into 129S7/SvEvBrd-Hprt1⁺-derived AB1 embryonic stem (ES) cells. Correctly targeted ES cells were injected into C57BL/6 blastocysts and the resulting chimeric males were bred to C57BL/6 females. These mice were intercrossed to establish a colony of p53 transgenic mice.

To generate the Brca1^F22-24 mutant allele, a targeting vector was designed by Dr. Alan Ashworth (Breakthrough Breast Cancer Research Centre, London) to replace exons 22-24 of the mouse breast cancer 1 gene (Brca1) with a loxP site, a cDNA sequence encoded by exons 22-24, a 3' myc epitope, bovine growth hormone polyA signal, a second loxP site, a splice acceptor sequence, and a PGK-neo cassette. This construct was electroporated into (129X1/SvJ x 129S1/Sv)F1-Kitl⁺-derived R1 embryonic stem (ES) cells. Correctly targeted ES cells were injected into C57BL/6J blastocysts and the resulting chimeric mice were bred to C57BL/6 mice. These mice were intercrossed to establish a colony of Brca1^{F22-24/F22-24} mice on a mixed background.

The BLG-Cre transgene was designed by Dr. Alan R. Clarke (while at University Medical School, Edinburgh, United Kingdom) to have Cre recombinase under the control of the sheep mammary gland specific promoter of the ovine beta-lactoglobulin (BLG) gene. The construct included exon 1 of sheep BLG, and a Cre recombinase with a modified initiation codon and a polyadenylation signal (polyA). The construct was microinjected into the pronuclei of (CBA x C57BL/6) fertilized oocytes, and mice from founder line 74 were identified and bred to C57BL/6 mice. These mice were intercrossed to establish a colony of BLG-cre mice on a mixed background.

Mutant mice were bred together to generate the triple mutant colony. Mice heterozygous for the p53 allele, homozygous for the floxed Brca1 allele (Brca1^{F22-24/F22-24}), and hemizygous for the BLG-cre transgene (also called BLG-Cre; Brca1^{F22-24/F22-24}; p53^+/- mice) were maintained on a mixed genetic background prior to sending to The Jackson Laboratory Repository. Upon arrival, mice were bred to C57BL/6J inbred mice (Stock No. 000664) for at least one generation to establish the colony.

Allele

Symbol: Tg(LGB-cre)74Acl
Name: transgene insertion 74, Alan R Clarke
MGI accession ID: MGI:2137694
Generation method: Transgenic
Attributes: Recombinase-expressing
Marker symbol: Tg(LGB-cre)74Acl
Marker name: transgene insertion 74, Alan R Clarke
Chromosome: UN
Strain of origin: (CBA x C57BL/6)
Expressed genes: cre,cre recombinase,bacteriophage P1
Site of expression: Cre recombinase is active in the mammary gland.
Molecular note: This transgene expresses Cre recombinase under the control of a sheep beta-lactoglobulin promoter (LGB), active in the mammary gland.

Allele

Symbol: Trp53^tm1Brd
Name: targeted mutation 1, Allan Bradley
MGI accession ID: MGI:1857590
Generation method: Targeted
Attributes: Null/Knockout
Marker symbol: Trp53
Marker name: transformation related protein 53
Chromosome: 11
Strain of origin: 129S7/SvEvBrd-Hprt⁺
Site of expression: Normal Trp53 expression is widespread.
Molecular note: A PolII-neomycin resistance cassette which lacked a polyadenylation signal was inserted into exon 5 of the gene. The insertion was accompanied by a small deletion of a 450 bp fragment containing 106 nucleotides of exon 5 and 350 nucleotides of intron 4.

Allele

Symbol: Brca1^tm1Aash
Name: targeted mutation 1, Alan Ashworth
MGI accession ID: MGI:3706167
Generation method: Targeted
Attributes: Conditional ready (e.g. floxed); No functional change
Marker symbol: Brca1
Marker name: breast cancer 1, early onset
Chromosome: 11
Strain of origin: (129X1/SvJ x 129S1/Sv)F1-Kitl⁺
Site of expression: mammary epithelial cells
Molecular note: Exons 22-24 were replaced with a floxed sequence containing cDNA for exons 22-24 with an in frame myc epitope and a bovine growth hormone poly A sequence. This vector allows conditional excision of the second, terminal BRCT domain. Downstream of the floxed sequence, a splice acceptor and PGK-neo were inserted.