Publications by authors named "Suzanne A Hartford"

9 Publications

  • Page 1 of 1

Interaction with PALB2 Is Essential for Maintenance of Genomic Integrity by BRCA2.

PLoS Genet 2016 08 4;12(8):e1006236. Epub 2016 Aug 4.

Mouse Cancer Genetics Program, Center for Cancer Research, National Cancer Institute, Frederick, Maryland, United States of America.

Human breast cancer susceptibility gene, BRCA2, encodes a 3418-amino acid protein that is essential for maintaining genomic integrity. Among the proteins that physically interact with BRCA2, Partner and Localizer of BRCA2 (PALB2), which binds to the N-terminal region of BRCA2, is vital for its function by facilitating its subnuclear localization. A functional redundancy has been reported between this N-terminal PALB2-binding domain and the C-terminal DNA-binding domain of BRCA2, which undermines the relevance of the interaction between these two proteins. Here, we describe a genetic approach to examine the functional significance of the interaction between BRCA2 and PALB2 by generating a knock-in mouse model of Brca2 carrying a single amino acid change (Gly25Arg, Brca2G25R) that disrupts this interaction. In addition, we have combined Brca2G25R homozygosity as well as hemizygosity with Palb2 and Trp53 heterozygosity to generate an array of genotypically and phenotypically distinct mouse models. Our findings reveal defects in body size, fertility, meiotic progression, and genome stability, as well as increased tumor susceptibility in these mice. The severity of the phenotype increased with a decrease in the interaction between BRCA2 and PALB2, highlighting the significance of this interaction. In addition, our findings also demonstrate that hypomorphic mutations such as Brca2G25R have the potential to be more detrimental than the functionally null alleles by increasing genomic instability to a level that induces tumorigenesis, rather than apoptosis.
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http://dx.doi.org/10.1371/journal.pgen.1006236DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4973925PMC
August 2016

Hypersensitivity of primordial germ cells to compromised replication-associated DNA repair involves ATM-p53-p21 signaling.

PLoS Genet 2014 Jul 10;10(7):e1004471. Epub 2014 Jul 10.

Department of Biomedical Sciences, Cornell University, Ithaca, New York, United States of America.

Genome maintenance in germ cells is critical for fertility and the stable propagation of species. While mechanisms of meiotic DNA repair and chromosome behavior are well-characterized, the same is not true for primordial germ cells (PGCs), which arise and propagate during very early stages of mammalian development. Fanconi anemia (FA), a genomic instability syndrome that includes hypogonadism and testicular failure phenotypes, is caused by mutations in genes encoding a complex of proteins involved in repair of DNA lesions associated with DNA replication. The signaling mechanisms underlying hypogonadism and testicular failure in FA patients or mouse models are unknown. We conducted genetic studies to show that hypogonadism of Fancm mutant mice is a result of reduced proliferation, but not apoptosis, of PGCs, resulting in reduced germ cells in neonates of both sexes. Progressive loss of germ cells in adult males also occurs, overlaid with an elevated level of meiotic DNA damage. Genetic studies indicated that ATM-p53-p21 signaling is partially responsible for the germ cell deficiency.
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http://dx.doi.org/10.1371/journal.pgen.1004471DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4091704PMC
July 2014

Minichromosome maintenance helicase paralog MCM9 is dispensible for DNA replication but functions in germ-line stem cells and tumor suppression.

Proc Natl Acad Sci U S A 2011 Oct 10;108(43):17702-7. Epub 2011 Oct 10.

Department of Biomedical Sciences and Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA.

Effective DNA replication is critical to the health and reproductive success of organisms. The six MCM2-7 proteins, which form the replicative helicase, are essential for high-fidelity replication of the genome. Many eukaryotes have a divergent paralog, MCM9, that was reported to be essential for loading MCM2-7 onto replication origins in the Xenopus oocyte extract system. To address the in vivo role of mammalian MCM9, we created and analyzed the phenotypes of mice with various mutations in Mcm9 and an intronic DNA replication-related gene Asf1a. Ablation of Mcm9 was compatible with cell proliferation and mouse viability, showing that it is nonessential for MCM2-7 loading or DNA replication. Mcm9 mutants underwent p53-independent embryonic germ-cell depletion in both sexes, with males also exhibiting defective spermatogonial stem-cell renewal. MCM9-deficient cells had elevated genomic instability and defective cell cycle reentry following replication stress, and mutant animals were prone to sex-specific cancers, most notably hepatocellular carcinoma in males. The phenotypes of mutant mice and cells suggest that MCM9 evolved a specialized but nonessential role in DNA replication or replication-linked quality-control mechanisms that are especially important for germ-line stem cells, and also for tumor suppression and genome maintenance in the soma.
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http://dx.doi.org/10.1073/pnas.1113524108DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3203795PMC
October 2011

A-MYB (MYBL1) transcription factor is a master regulator of male meiosis.

Development 2011 Aug;138(15):3319-30

Cornell University College of Veterinary Medicine, Department of Biomedical Sciences, Center for Vertebrate Genomics, Ithaca, NY 14850, USA.

The transcriptional regulation of mammalian meiosis is poorly characterized, owing to few genetic and ex vivo models. From a genetic screen, we identify the transcription factor MYBL1 as a male-specific master regulator of several crucial meiotic processes. Spermatocytes bearing a novel separation-of-function allele (Mybl1(repro9)) had subtle defects in autosome synapsis in pachynema, a high incidence of unsynapsed sex chromosomes, incomplete double-strand break repair on synapsed pachytene chromosomes and a lack of crossing over. MYBL1 protein appears in pachynema, and its mutation caused specific alterations in expression of diverse genes, including some translated postmeiotically. These data, coupled with chromatin immunoprecipitation (ChIP-chip) experiments and bioinformatic analysis of promoters, identified direct targets of MYBL1 regulation. The results reveal that MYBL1 is a master regulator of meiotic genes that are involved in multiple processes in spermatocytes, particularly those required for cell cycle progression through pachynema.
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http://dx.doi.org/10.1242/dev.067645DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3133921PMC
August 2011

The dual bromodomain and WD repeat-containing mouse protein BRWD1 is required for normal spermiogenesis and the oocyte-embryo transition.

Dev Biol 2008 May 21;317(1):72-82. Epub 2008 Feb 21.

Cornell University, College of Veterinary Medicine, Ithaca, NY 14850, USA.

A novel mutation, repro5, was isolated in a forward genetic screen for infertility mutations induced by ENU mutagenesis. Homozygous mutant mice were phenotypically normal but were infertile. Oocytes from mutant females appeared normal, but were severely maturation-defective in that they had reduced ability to progress to metaphase II (MII), and those reaching MII were unable to progress beyond the two pronuclei stage following in vitro fertilization (IVF). Mutant males exhibited defective spermiogenesis, resulting in oligoasthenoteratospermia. Genetic mapping, positional cloning, and complementation studies with a disruption allele led to the identification of a mutation in Brwd1 (Bromodomain and WD repeat domain containing 1) as the causative lesion. Bromodomain-containing proteins typically interact with regions of chromatin containing histones hyperacetylated at lysine residues, a characteristic of chromatin in early spermiogenesis before eventual replacement of histones by the protamines. Previous data indicated that Brwd1 is broadly expressed, encoding a putative transcriptional regulator that is believed to act on chromatin through interactions with the Brg1-dependent SWI/SNF chromatin-remodeling pathway. Brwd1 represents one of a small number of genes whose elimination disrupts gametogenesis in both sexes after the major events of meiotic prophase I have been completed.
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http://dx.doi.org/10.1016/j.ydbio.2008.02.018DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2475337PMC
May 2008

A viable allele of Mcm4 causes chromosome instability and mammary adenocarcinomas in mice.

Nat Genet 2007 Jan 3;39(1):93-8. Epub 2006 Dec 3.

Department of Genetics, Cell Biology and Development, College of Biological Sciences, University of Minnesota, Minneapolis, Minnesota 55455, USA.

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. Mcm4(Chaos3) 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, Mcm(Chaos3/-) embryos died late in gestation, indicating that Mcm4(Chaos3) is hypomorphic. Mutant embryonic fibroblasts were highly susceptible to chromosome breaks induced by the DNA replication inhibitor aphidicolin. Most notably, >80% of Mcm4(Chaos3/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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http://dx.doi.org/10.1038/ng1936DOI Listing
January 2007

Random mutagenesis of proximal mouse chromosome 5 uncovers predominantly embryonic lethal mutations.

Genome Res 2005 Aug 15;15(8):1095-105. Epub 2005 Jul 15.

The Jackson Laboratory, Bar Harbor, Maine 04609, USA.

A region-specific ENU mutagenesis screen was conducted to elucidate the functional content of proximal mouse Chr 5. We used the visibly marked, recessive, lethal inversion Rump White (Rw) as a balancer in a three-generation breeding scheme to identify recessive mutations within the approximately 50 megabases spanned by Rw. A total of 1003 pedigrees were produced, representing the largest inversion screen performed in mice. Test-class animals, homozygous for the ENU-mutagenized proximal Chr 5 and visibly distinguishable from nonhomozygous littermates, were screened for fertility, hearing, vestibular function, DNA repair, behavior, and dysmorphology. Lethals were identifiable by failure to derive test-class animals within a pedigree. Embryonic lethal mutations (total of 34) were overwhelmingly the largest class of mutants recovered. We characterized them with respect to the time of embryonic death, revealing that most act at midgestation (8.5-10.5) or sooner. To position the mutations within the Rw region and to guide allelism tests, we performed complementation analyses with a set of new and existing chromosomal deletions, as well as standard recombinational mapping on a subset of the mutations. By pooling the data from this and other region-specific mutagenesis projects, we calculate that the mouse genome contains approximately 3479-4825 embryonic lethal genes, or about 13.7%-19% of all genes.
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http://dx.doi.org/10.1101/gr.3826505DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1182222PMC
August 2005

Toward the genetics of mammalian reproduction: induction and mapping of gametogenesis mutants in mice.

Biol Reprod 2003 Nov 9;69(5):1615-25. Epub 2003 Jul 9.

The Jackson Laboratory, Bar Harbor, Maine 04609, USA.

The genetic control of mammalian gametogenesis is inadequately characterized because of a lack of mutations causing infertility. To further the discovery of genes required for mammalian gametogenesis, phenotype-driven screens were performed in mice using random chemical mutagenesis of whole animals and embryonic stem cells. Eleven initial mutations are reported here that affect proliferation of germ cells, meiosis, spermiogenesis, and spermiation. Nine of the mutations have been mapped genetically. These preliminary studies provide baselines for estimating the number of genes required for gametogenesis and offer guidance in conducting new genetic screens that will accelerate and optimize mutant discovery. This report demonstrates the efficacy and expediency of mutagenesis to identify new genes required for mammalian gamete development.
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http://dx.doi.org/10.1095/biolreprod.103.019877DOI Listing
November 2003

Phenotype-based identification of mouse chromosome instability mutants.

Genetics 2003 Mar;163(3):1031-40

The Jackson Laboratory, Bar Harbor, Maine 04609, USA.

There is increasing evidence that defects in DNA double-strand-break (DSB) repair can cause chromosome instability, which may result in cancer. To identify novel DSB repair genes in mice, we performed a phenotype-driven mutagenesis screen for chromosome instability mutants using a flow cytometric peripheral blood micronucleus assay. Micronucleus levels were used as a quantitative indicator of chromosome damage in vivo. Among offspring derived from males mutagenized with the germline mutagen N-ethyl-N-nitrosourea (ENU), we identified a recessive mutation conferring elevated levels of spontaneous and radiation- or mitomycin C-induced micronuclei. This mutation, named chaos1 (chromosome aberration occurring spontaneously 1), was genetically mapped to a 1.3-Mb interval on chromosome 16 containing Polq, encoding DNA polymerase theta. We identified a nonconservative mutation in the ENU-derived allele, making it a strong candidate for chaos1. POLQ is homologous to Drosophila MUS308, which is essential for normal DNA interstrand crosslink repair and is unique in that it contains both a helicase and a DNA polymerase domain. While cancer susceptibility of chaos1 mutant mice is still under investigation, these data provide a practical paradigm for using a forward genetic approach to discover new potential cancer susceptibility genes using the surrogate biomarker of chromosome instability as a screen.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1462482PMC
March 2003