B6N.129S6(SJL)-Jak2^tm1.1Ble/AmlyJ

Stock number: 031658
Product name: Jak2^Fl
Research areas: Cell Biology Research, Immunology, Inflammation and Autoimmunity Research, Research Tools

Description

Jak2^+/Fl mice have an inverted exon 14, carrying a valine to phenylalanine mutation (V617F), downstream of the endogenous exon 14 of the Janus kinase 2 (Jak2) gene. Both exons are surrounded by loxP and loxP511 sites, allowing for Cre-mediated removal of the endogenous exon 14 and inversion of the mutated exon 14. These mice may be useful when studying myeloproliferative neoplasm (MPN).

Detailed description

Jak2^+/Fl mice have an inverted exon 14, carrying a valine to phenylalanine mutation (V617F), downstream of the endogenous exon 14 of the Janus kinase 2 (Jak2) gene. Both exons are surrounded by loxP and loxP511 sites, allowing for Cre-mediated removal of the endogenous exon 14 and inversion of the mutated exon 14. The V617F mutation is commonly found in patients with myeloproliferative neoplasm (MPN) and is present in approximately 95% of patients with polycythemia vera (PV) and in approximately 50% of patients with essential thrombocythemia (ET) and primary myelofibrosis (PMF).

JAK2 is a protein tyrosine kinase involved in a specific subset of cytokine receptor signaling pathways and is misregulated or mutated in some myeloproliferative diseases and cancers. The V617F mutation results in constitutive activation of JAK2 kinase signaling. When activated, JAK2 phosphorylates STAT transcription factors and initiates the JAK-STAT signaling pathway. This is the most prevalent JAK2 mutation.

Mice that are heterozygous for this allele are viable and fertile, while floxed homozygous mice are not viable. Lethality may be the result of the targeting construct creating a null allele prior to cre excision. When bred to mice that express tissue-specific Cre recombinase, resulting offspring will have the floxed endogenous exon 14 removed and the V617F mutant exon 14 placed into correct transcriptional orientation.

When mice are bred to a germline or a hematopoietic-specific Cre Recombinase expressing strain such as B6.FVB-Tg(EIIa-cre)C5379Lmgd/J (Stock No. 003724), B6.Cg-Tg(Mx1-cre)1Cgn/J (Stock No. 003556), or VavCre, mice are a model of MPN characterized by elevated hematocrit (HCT), splenomegaly, and prominent splenic extramedullary erythropoiesis. Mice have median survival time of 146 days. They develop lethal 100% penetrant myeloproliferative neoplasms but not acute leukemia. The bone marrow myeloid progenitor compartment is skewed toward the erythroid lineage, which cannot transfer disease. The long-term HSC compartment (CD150+ CD48+ LSK) can transplant the disease into lethally irradiated wild-type recipient mice. When mice are treated with Interferon-α, Jak2^VF MPN-propagating cells are depleted, and the disease cannot be transferred.

Of note crossing primary floxed mice to MxCre results in spontaneous recombination in the absence of pIpC.

Development

The Jak2^Fl targeting vector was designed to insert an inverted mutated exon 14 downstream of endogenous exon 14 of the Janus kinase 2 (Jak2) gene. Specifically, the vector included, from 5’ to 3', a loxP site, endogenous exon 14, a loxP511 site, an inverted exon 14, a second loxP site and a second loxP511 site. The inverted exon 14 was modified to harbor a guanine to thymine substitution (G1849T) at amino acid 617, resulting in a valine to phenylalanine mutation (V617F), commonly found in patients with myeloproliferative neoplasm (MPN). An FRT-flanked neomycin resistance (neo) cassette was placed directly downstream of the second loxP511 site. The construct was electroporated into 129S6/SvEvTac-derived TC-1 embryonic stem (ES) cells. ES cells were injected into blastocysts and resulting chimeras were mated to C57BL/6 mice. Offspring were subsequently bred to ACTB:FLPe mice (Stock No. 005703) to remove the neo cassette and progeny were crossed to remove the Flpe-expressing transgene. Jak2^+/Fl mice were bred to C57BL/6NCrl mice for at least 10 generations. Upon arrival at The Jackson Laboratory Repository, sperm was cryopreserved. To establish our live colony, an aliquot of frozen sperm was used to fertilize C57BL/6NJ oocytes (Stock No. 005304).

Allele

Symbol: Jak2^tm1.1Ble
Name: targeted mutation 1.1, Benjamin L Ebert
MGI accession ID: MGI:4818800
Generation method: Targeted
Attributes: Conditional ready (e.g. floxed)
Marker symbol: Jak2
Marker name: Janus kinase 2
Chromosome: 19
Strain of origin: 129S6/SvEvTac
Molecular note: A loxP site was inserted upstream of exon 14 and a cassette, consisting of a loxP511 site, a linker, an inverted loxP site, an inverted exon 14 containing a G1849T mutation, an inverted loxP511 site, and an FRT flanked neo selection cassette, was inserted downstream of exon 14 via homologous recombination. The neo cassette was removed by flp mediated recombination. The targeting cassette appears to interfere with endogenous gene expression making this a null allele.