C57BL/6-Flt3^{tm1.1(FLT3*)Rlvn}/J

Stock number: 036725
Product name: Flt3^Frt-ITD

Research areas: Cancer Research, Research Tools

Description

Flt3^Frt-ITD mice conditionally express a humanized W51 FLT3 (FMS-like tyrosine kinase 3) internal tandem duplication (ITD). Upon the expression of widely-expressed FLP recombinase, wildtype protein expression is replaced with that of the mutant form and mice develop a myeloproliferative disease.

Detailed description

Flt3 (FMS-like tyrosine kinase 3) is the most commonly mutated gene in acute myeloid leukemia (AML). Internal tandem duplication (ITD) mutations in the gene occur late in leukemic transformation.

Flt3^Frt-ITD mice conditionally express a humanized W51 FLT3 ITD (a duplication of amino acids 596 to 602; PMID:17936561). When crossed with mice expressing tamoxifen-inducible Flp recombinase from a broadly expressed CAG promoter (see Stock No. 019016, B6N.129S6(Cg)-Gt(ROSA)26Sor^{tm3(CAG-flpo/ERT2)Alj}/J), tamoxifen treatment results in wildtype protein expression being replaced with that of the mutant form. Compound heterozygous mutant mice expressing the W51 ITD develop penetrant leukocytosis by 6 weeks of age. By 8-10 weeks, this leukocytosis is largely resolved, with white blood cells (WBCs) decreasing to near normal levels despite persistent anemia and thrombocytopenia. The tamoxifen-treated compound mutant mice develop significant splenomegaly and a pathological myeloid infiltrate into both the spleen and liver. An increase in immature myeloid cells, reduction in megakaryocytes, and near absence of erythroid cells is evident in the bone marrow.

Development

An FRT site (inverted) was placed in intron 12, and a lox2272-flanked neomycin cassette followed by an inversion cassette was introduced downstream of 15 of the mouse Flt3 gene by homologous recombination in C57BL/6-derived embryonic stem cells. The inversion cassette, carrying exons 13, 14*, and 15 (in reverse orientation) followed by an FRT site, is flanked by two divergent, outward-facing F3 sites. Exon 14* of the inversion cassette is modified to express humanized FLT3-ITD W51 (a duplication of amino acids 596 to 602; PMID:17936561). Flanking genomic sequences from upstream of exon 13 to downstream of exon 15 surround the inversion cassette for correct splicing (Inv.saE13-14*-E15Sd). The neomycin cassette was excised by transient expression of Cre recombinase in the targeted ES cells. The donating laboratory maintained this strain on a C57BL/6 genetic background prior to providing one vial frozen sperm to The Jackson Laboratory Repository in 2025. Upon using that sperm to to fertilize C57BL/6J oocytes (Stock No. 000664), the resulting recovered mice that were negative for FLPo/neo were chosen as live colony founders. Subsequently, sperm was cryopreserved.

In 2025, 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 mice provided to The Jackson Laboratory Repository. While 42 of the 43 markers throughout the genome suggested a C57BL/6 genetic background, one marker on Chromosome 18 (~81 Mb) was segregating for allele-type other than C57BL/6. These data suggest the mice sent to The Jackson Laboratory Repository were on a C57BL/6 genetic background with an unknown genetic contribution on Chromosome 18.

Allele

Symbol: Flt3^{tm1.1(FLT3*)Rlvn}
Name: targeted mutation 1.1, Ross Levine
MGI accession ID: MGI:7768128
Generation method: Targeted
Attributes: Conditional ready (e.g. floxed); Inserted expressed sequence; Humanized sequence
Marker symbol: Flt3
Marker name: FMS-like tyrosine kinase 3
Marker synonyms: CD135; FLK2; FLK-2; Flt-3; STK1; wmfl
Chromosome: 5
Strain of origin: C57BL/6
Molecular note: An FRT site (inverted) was placed in intron 12, and a lox2272-flanked neomycin cassette followed by an inversion cassette was introduced downstream of 15 of the mouse Flt3 gene by homologous recombination in C57BL/6-derived embryonic stem cells. The inversion cassette, carrying exons 13, 14*, and 15 (in reverse orientation) followed by an FRT site, is flanked by two divergent, outward-facing F3 sites. Exon 14* of the inversion cassette is modified to express humanized FLT3-ITD W51 (a duplication of amino acids 596 to 602. Flanking genomic sequences from upstream of exon 13 to downstream of exon 15 surround the inversion cassette for correct splicing (Inv.saE13-14*-E15Sd). The neomycin cassette was excised by transient expression of cre recombinase in the targeted ES cells.