B6N.Cg-Kras^tm4Tyj/CjDswJ

Stock number: 019104

Description

This LSL-KrasG12D strain carries a point mutation (G12D) in the Kras (v-Ki-ras2 Kirsten rat sarcoma viral oncogene homolog) gene whose expression is blocked by the presence of a loxP-flanked stop codon. Homozygotes die in utero. Cre-mediated recombination can excise the stop codon and permit the oncogenic protein to be expressed. Intranasal infection with an adenovirus encoding Cre results in a very high frequency of lung tumors and permits controlled timing of tumor initiation and tumor multiplicity. This strain may be useful in studies of cancer and development.

Detailed description

This strain carries a point mutation (G12D) whose expression is blocked by the presence of a loxP-flanked stop codon. Homozygotes die in utero. Cre-mediated recombination can excise the stop codon and permit the oncogenic protein to be expressed. Intranasal infection with an adenovirus encoding Cre results in a very high frequency of lung tumors and permits controlled timing of tumor initiation and tumor multiplicity. This strain may be useful in studies of cancer and development.

In an attempt to offer alleles on well-characterized or multiple genetic backgrounds, alleles are frequently moved to a genetic background different from that on which an allele was first characterized. This is the case for the strain above. It should be noted that the phenotype could vary from that originally described. We will modify the strain description if necessary as published results become available.

Development

A targeting vector was designed to place a G12D point mutation in exon 1 of the gene and a loxP-flanked STOP element upstream of the mutation. The STOP element incorporates a PGK-puromycin selection cassette at the 5' end in an opposite directional orientation. An adenoviral strong splice acceptor, typically used in gene trap vectors, is fused upstream of the his3 stuffer fragment to prevent splicing around the stopper (in the case that transcription isn't completely silenced). A mutant splice donor site is on the 3' end and a tetrameric tandem array of SV40 PolyA. The stopper was designed to fit into genomic Sal1 or Xho1 sites. The stop cassette prevents the expression of mutant Kras until it is removed by Cre mediated recombination of the Loxp sites, thus allowing expression of oncogenic Kras. The construct was electroporated into 129S4/SvJae-derived J1 embryonic stem (ES) cells. The mice were backcrossed to C57BL/6 for approximately 15 generations (NCI) and then backcrossed to C57BL/6NCr for 19 generations. Upon arrival at The Jackson Laboratory, the mice were crossed to C57BL/6NJ (Stock No. 005304) at least once to establish the colony.

Allele

Symbol: Kras^tm4Tyj
Name: targeted mutation 4, Tyler Jacks
MGI accession ID: MGI:2429948
Generation method: Targeted
Attributes: Conditional ready (e.g. floxed); No functional change
Marker symbol: Kras
Marker name: Kirsten rat sarcoma viral oncogene homolog
Chromosome: 6
Strain of origin: 129S4/SvJae
Site of expression: Cre-inducible expression of oncogenic Kras^G12D protein
Molecular note: By homologous recombination in ES cells, the Kras2 locus was targeted with a cassette containing an oncogenic form of the KRAS2 protein in which the glycine at position 12 had been substituted with a an aspartic acid. A loxP flanked stop codon was included upstream of the inserted Kras2 sequence, such that the mutant transcript would be expressed only after cre-mediated recombination.