Mice homozygous for this ENU-induced F345I hypomorphic allele (Chaos3) are viable, fertile, and overtly indistinguishable from normal littermates. Homozygous, but not heterozygous, mice have slightly reduced wildtype protein levels in mouse embryonic fibroblasts (MEFs). Whereas Chaos3 heterozygotes show mildly elevated (2- to 5-fold) micronucleus frequencies compared with wildtype, homozygotes have an approximate 20-fold increase with over 7% of erythrocytes containing micronuclei. MEFs from homozygous mice exhibit mild defects (cell proliferation, S phase and G2/M populations), and are highly susceptible to chromosome breakage following treatment with the DNA replication inhibitor aphidicolin. On a congenic C3HeB/FeJ background, greater than 80% of homozygous females exhibit mammary adenocarcinomas with a mean latency of 12 months, while males have no tumor incidence. These Chaos3 mice provide a novel, non-transgenic model of breast cancer, and may be useful for studying of diagnostic pre-cancer cell markers, chromosomal instability and cell cycle checkpoint responses.
Male C57BL/6J mice (Stock No. 000664) were treated with multidose N-ethyl-N-nitrosourea (ENU) and then bred to C3HeB/FeJ (Stock No. 000658). The resulting male pups were then bred to C3HeB/FeJ females to obtain second generation mice, which were subsequently intercrossed to obtain third generation mice. A mutagenesis screen was then performed to select mice for chromosome instability (as assessed by micronucleus levels in erythrocytes). One of these mutants in which the tendency to form micronuclei segregated in a monogenic, autosomal recessive manner was termed Chaos3 (or chromosome aberrations occurring spontaneously 3). Further studies revealed that Chaos3 is a hypomorphic allele of Mcm4, containing a T to A transversion at nucleotide 1033 of the coding region that defines an amino acid change from phenylalanine to isoleucine at residue 345 (F345I). These mice have been backcrossed to C3HeB/FeJ for at least 8 generations prior to arrival at The Jackson Laboratory.
|Allele Name||chromosomal aberration occurring spontaneously 3|
|Allele Type||Chemically induced (ENU)|
|Allele Synonym(s)||Chaos3; Mcm4F345I|
|Gene Symbol and Name||Mcm4, minichromosome maintenance complex component 4|
|Strain of Origin||C57BL/6J|
|Molecular Note||In an ENU mutagenesis screen, a de novo T->A transversion at nucleotide 1033 of the coding region occurred, creating a phenylalanine to isoleucine change at residue 345.|
|Mutations Made By|| |
John Schimenti, Cornell University
When maintaining a live colony, heterozygous mice are bred to C3HeB/FeJ (Stock No. 000658) inbred mice or wildtype siblings. Homozygous mutant females develop mammary turmors with a high incidence by approximately one year of age. Breeding productivity in heterozygous female may decline with age.
When using the Chaos3 mouse strain in a publication, please cite the originating article(s) and include JAX stock #006863 in your Materials and Methods section.