Abstract
Mcm4 (minichromosome maintenance–deficient 4 homolog) encodes a subunit of the MCM2-7 complex (also known as MCM2–MCM7), the replication licensing factor and presumptive replicative helicase. Here, we report that the mouse chromosome instability mutation Chaos3 (chromosome aberrations occurring spontaneously 3), isolated in a forward genetic screen, is a viable allele of Mcm4. Mcm4Chaos3 encodes a change in an evolutionarily invariant amino acid (F345I), producing an apparently destabilized MCM4. Saccharomyces cerevisiae strains that we engineered to contain a corresponding allele (resulting in an F391I change) showed a classical minichromosome loss phenotype. Whereas homozygosity for a disrupted Mcm4 allele (Mcm4−) caused preimplantation lethality, McmChaos3/− embryos died late in gestation, indicating that Mcm4Chaos3 is hypomorphic. Mutant embryonic fibroblasts were highly susceptible to chromosome breaks induced by the DNA replication inhibitor aphidicolin. Most notably, >80% of Mcm4Chaos3/Chaos3 females succumbed to mammary adenocarcinomas with a mean latency of 12 months. These findings suggest that hypomorphic alleles of the genes encoding the subunits of the MCM2-7 complex may increase breast cancer risk.
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Acknowledgements
We thank B.S. Collins for assistance with mouse necropsy, K. Schimenti for help with flow cytometric analysis and I. Mikaelian for initial pathological analysis. This work was supported by grant R01 GM45415 from the US National Institutes of Health to J.C.S. N.S. was a recipient of Department of Defense Breast Cancer Research fellowship DAMD 17-01-1-0277.
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The technical design, gene identification and model characterization were conducted primarily by N.S.; A.A. performed pathology analysis; I.L. conducted the yeast analyses using a construct made by S.A.H., and both were overseen by B.K.T.; T.R.B. and C.A. conducted protein and cell cycle analyses; R.M. performed embryonic stem cell culture and microinjections and J.S. oversaw the mutant screening project and was mentor to The Jackson Laboratory/Cornell team. The paper was co-written by N.S. and J.C.S.
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Supplementary information
Supplementary Fig. 1
Structure of the Mcm4 gene-trap allele. (PDF 94 kb)
Supplementary Fig. 2
Extended survival of Mcm4Chaos3/Mcm4− embryos in mixed backgrounds. (PDF 547 kb)
Supplementary Table 1
Genes in the Chaos3 critical region. (PDF 83 kb)
Supplementary Table 2
Spontaneous tumors in Mcm4Chaos3 homozygous mice. (PDF 53 kb)
Supplementary Table 3
Primers used for positional cloning and genotyping. (PDF 35 kb)
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Shima, N., Alcaraz, A., Liachko, I. et al. A viable allele of Mcm4 causes chromosome instability and mammary adenocarcinomas in mice. Nat Genet 39, 93–98 (2007). https://doi.org/10.1038/ng1936
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DOI: https://doi.org/10.1038/ng1936