Nbs1ΔB mice produce a truncated NBN protein lacking the BRCT domain. They may be useful when studying human chromosome instability syndromes such as Nijmegen Breakage Syndrome and ataxia-telangiectasia like disorder.
John Petrini, Memorial Sloan-Kettering Cancer Center
Nbs1ΔB mice have a floxed neo cassette replacing exons 4-5 of the nibrin (Nbn1) gene. NBN is a component of a trimeric protein complex also containing Mre11 and Rad50 which is involved in DNA double-strand break repair, cell cycle checkpoint activation, telomere maintenance, and meiotic recombination. Many Nbn mutations result in the production of a truncated protein missing regions required for effectively responding to DNA damage, resulting in a buildup of DNA strand breaks leading to radiation exposure sensitivity. Mutations in NBN have been found in patients with Nijmegen Breakage Syndrome (NBS), which is characterized by short stature, microcephaly, distinctive facial features, recurrent respiratory tract infections, an increased risk of cancer, and intellectual disability. Exons 4-5 encode the BRCT domain of NBN, removal of which causes a truncated 80 kDa isoform which is still capable of binding MRE11. Homozygous Nbs1Ddelta;B mice are viable and fertile. However, the Donating Investigator reports that female homozygotes may be infertile. Homozygotes are sensitive to gamma-irradiation and are prone to tumor development. Mouse embryonic fibroblasts (MEFs) from these mice exhibit defective cell cycle checkpoints after radiation.
A targeting vector was designed to replace exons 4-5, encoding the BRCT domain, of the nibrin (Nbn1) gene with a loxP-flanked neomycin resistance (neo) in reverse orientation to the gene. The construct was electroporated into 129S7/SvEvBrd-Hprtb-m2-derived AB2.2 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 backcrossed at least 5 generations to C57BL/6 mice (see SNP note below). Upon arrival at The Jackson Laboratory, mice were bred to C57BL/6J (Stock No. 000664) for at least one generation to establish the colony.
A 32 SNP (single nucleotide polymorphism) panel analysis, with 27 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 27 markers throughout the genome were segregating suggesting an incomplete backcross. Also, 2 of 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/6J ; C57BL/6N genetic background.
|Allele Name||targeted mutation 1, John H J Petrini|
|Allele Type||Targeted (Null/Knockout)|
|Gene Symbol and Name||Nbn, nibrin|
|Strain of Origin||129S7/SvEvBrd-Hprtb-m2|
|Molecular Note||Exons 4 and 5 were replaced with a floxed PGK-neo cassette via homologous recombination resulting in the deletion of the BRCT domain. An 80 kDa protein was expressed from the mutant allele as a result of a start codon originating in the PGK-neo cassette and splicing from intron 5 to exon 6. The mutant protein lacks the FHA and BRCT domains and retains Mre11a-binding activity.|
When maintaining a live colony, homozygotes may be bred together. However, the Donating Investigator reports that female homozygotes may be infertile.
When using the B6;129S7-Nbntm1Jpt/J mouse strain in a publication, please cite the originating article(s) and include JAX stock #024335 in your Materials and Methods section.