John Schimenti

Overview

My laboratory uses the mouse as a model system to investigate the genetics of mammalian development, gametogenesis, and cancer. We have used forward and reverse genetic technologies to mutagenize the mouse genome and identify novel genes involved in these processes.

In one project, we conducted a forward genetic screen for mice carrying mutations that cause chromosome instability (CIN). CIN is a hallmark of cancer cells, and in some cases, may be a causative defect leading to cancers. One of the mutations we recovered caused a 20 fold elevation in CIN. Positional cloning revealed that the mutation is a hypomorphic allele of an essential and highly conserved DNA replication gene called Mcm4. Whereas null mutations are lethal, our allele, called Chaos3, encodes a single amino acid change in an absolutely conserved residue, allowing the mice to be viable. However, female mice with this mutation are highly susceptible to mammary tumors exclusively; about 80% get aggressive mammary adenocarcinomas by 1 year of age. This mouse is a uniquenon-transgenic model of breast cancer, and suggests that variants in DNA replication genes may constitute a previously unrecognized basis for certain cancers. We are investigate the molecular genetic pathways leading to cancer in Chaos3 mice, exploring the cause for the mammary specificity, and investigating the potential roles of other DNA replication genes in cancer.

With respect to gametogenesis, we concentrate on the process of meiosis. During meiosis, DNA is replicated, homologous chromosomes pair, recombination occurs, and two rounds of divisions follow to create haploid gametes. We have isolated several mutants that disrupt these steps, using both forward and reverse genetic strategies. Among the novel genes we are studying are : Mei1, a vertebrate-specific gene required for initation of meiotic recombination; Mei4, which is responsible for crossing over; and Trip13, a gene that is specifically required for noncrossover recombination. We are exploiting our collection of mutants to understand the “checkpoints” that monitor the fidelity of meiotic chromosome behavior. Finally, with my colleagues Mary Ann Handel and John Eppig at The Jackson Laboratory, we have established a “Reprogenomics” program (reprogenomics.jax.org) that has generated the world’s most extensive collection of mouse infertility mutants that we and others are studying.

The final major project in the lab addresses the functional genomic content of proximal mouse Chromosome 5, representing about 2% of the genome. A region-specific ENU mutagenesis screen was conducted, yielding 37 embryonic lethal mutations. We have determined the timing and phenotypes of death for most of them, which range from pre-implantation lethality to a late-gestation homeotic-like skeletal transformation, and have been identifying the underlying genes. This project is yielding insight into the functional elements in a representative portion of the mouse genome.

Research Focus

Dr. Schimenti's laboratory uses the laboratory mouse as a model system to investigate the genetics of mammalian development, gametogenesis, and maintenance of genome integrity. They use a variety of technologies to mutagenize the mouse genome to identify novel genes involved in these processes. With respect to gametogenesis, they concentrate on the process of meiosis. During meiosis, DNA is replicated, homologous chromosomes pair, recombination occurs, and two rounds of divisions follow to create haploid gametes. They have isolated several mutants that disrupt these steps, using chemical mutagenesis of embryonic stem (ES) cells and of the germline. One of them is called Mei1, which disrupts the process of chromosome synapsis (intimate pairing of homologous chromosomes). They found that Mei1 is required for the genetically-programmed induction of double strand breaks in meiotic chromosomes, which is the initiating event in recombination. Despite being required for such a fundamental process, this gene is unique to vertebrates. Another meiotic mutation they are studying is called mei4. This abolishes the formation of chiasmata, the sites of crossing over. In addition to their collection of meiotic mutants, they are investigating infertility mutations that affect earlier stages of germ cell production as well as postmeiotic sperm development.

In another project, a region-specific ENU mutagenesis screen was conducted to explore the functional content of proximal mouse Chromosome 5, representing about 2% of the genome. Embryonic lethal mutations (a total of 37) were overwhelmingly the largest class of mutants recovered. They have determined the timing and phenotypes of death for most of them, which range from pre-implantation lethality to a late-gestation homeotic-like skeletal transformation. To facilitate the mapping and cloning of these mutations in a systematic manner, they created a collection of nested chromosomal deletions in the region, using an ES cell-based technology. Failure of a deletion to complement a lethal mutation indicates the location of the defective gene.

A more recent project involves the isolation of mice having mutations causing genomic instability (GIN). GIN is a hallmark of cancer cells, but there is controversy over whether it is an early or late event or cancer progression. By isolating a collection of GIN mutants, they hope to address this issue and to potentially identify new cancer susceptibility genes. A mutagenesis screen was conducted for mice with GIN, using a flow cytometric screen for DNA fragmentation in blood cells. Of the two mutations that they've positionally cloned, one is polymerase theta (Polq), which appears to play a rather unique role in DNA repair. By placing this mutation into certain genetic backgrounds, tumor progression is either accelerated or delayed. The other is an allele of a DNA replication control gene, causing a 20 fold elevation in chromosome aberrations. Recent data indicates that mice with this mutation are highly susceptible to mammary tumors.

Publications

• Philipps, D., Wigglesworth, K., Hartford, S., Sun, F., Pattabiraman, S., Schimenti, K., Handel, M.A., Eppig, J.J. and Schimenti, J. (2008) The dual bromodomain and WD repeat-containing mouse protein BRWD1 is required for normal spermiogenesis and the oocyte-embryo transition. Devel Biol 317:72-82
• Ward, J., Reinholdt, L., Motley, W., Niswander, L., Deacon, D., Griffin, L., Langlais, K., Backus, V., Schimenti, K., O’Brien, M., Eppig, J. and Schimenti, J. (2007) Mutation in mouse Hei10, an E3 ubiquitin ligase, disrupts meiotic crossing-over. PloS Genetics 3: e139.
• Li, X. and Schimenti, J. Mouse Pachytene Checkpoint 2 (Trip13) is required for completing meiotic recombination but not synapsis. (2007) PLoS Genetics 3:e130.
• Harris, T., Marquez, B., Suarez, S. and Schimenti, J. (2007) Sperm motility defects and infertility in male mice with a mutation in Nsun7, a member of the SUN domain-containing family of putative RNA methyltransferases. Biol. Reprod. 77: 376-382. Shima, N., Buske, T. and Schimenti, J. (2007) Genetic screen for chromosomal instability in mice: Mcm4 and breast cancer. Cell Cycle 6: 1135-1140.
• Bannister, L., Pezza, R., Donaldson, J., de Rooij, D., Schimenti, K., Camerini-Otero, D. and Schimenti, J. (2007) Male-specific sterility in mice carrying a dominant, recombination-defective allele of the RecA homolog Dmc1. PLoS Biology 5:e105.
• Howell, G., Shindo, M., Murray, S., Gridley, T. Wilson, L. and Schimenti, J. (2007) Mutation of an ubiquitously-expressed mouse transmembrane protein (Tapt1) causes specific skeletal homeotic transformations. Genetics 175:699-707.
• Shima, N., Alcaraz, A., Liachko, I., Buske, T., Andrews, C., Munroe, R., Hartford, S., Tye, B., and Schimenti, J. (2007) A viable mutation of Mcm4Nature Genetics causes genomic instability and mammary adenocarcinoma in mice. 19: 93-98.
• Lessard, C., Lothrop, H., Schimenti, J. and Handel, M.A. (2007) Mutagenesis-generated mouse models of human infertility with abnormal sperm. Human Reproduction, 22: 159-166.
• Reinholdt, L., Munroe, R., Kamdar, S. and Schimenti, J. (2006) The mouse gcd2 mutation causes primordial germ cell depletion. Mechanisms of Development 123: 559-569.
• Zan, H., Shima, N., Wu, Z., Al-Qahtani, A., Evinger, A., Zhong, Y., Schimenti , J. and Casali, P. (2005) The translesion DNA Polymerase Theta plays a dominant role in immunoglobulin gene somatic hypermutation. EMBO 24: 3757-59.
• Wilson, L, Ching, Y., Farias, M., Hartford, S., Howell, G., Shao, H., Bucan, M. and Schimenti, J. (2005) ENU mutagenesis of proximal mouse Chromosome 5 uncovers predominantly embryonic lethal mutations. Genome Research. 15:1095-1105.
• Reinholdt, L. and Schimenti, J. (2005) Mei1 is epistatic to Dmc1 in mouse meiosis. Chromosoma, 114: 127-134.
• Schimenti, J., Reynolds, J. and Planchart, A. (2005) Mutations in Serac1 or Synj2 cause proximal t haplotype –mediated male mouse sterility, but not transmission ratio distortion. PNAS 102: 3342-3347.
• Bannister , L, Reinholdt, L. Munroe, R. and Schimenti, J. (2004) Positional cloning and characterization of mouse mei8, a disrupted allele of the meiotic cohesin Rec8. Genesis, 40: 184-194. (Cover).
• Shima, N. Munroe, R. and Schimenti, J. (2004) The mouse genomic instability mutation chaos1 is an allele of Polq that exhibits genetic interaction with Atm. Mol. Cell. Biol. 24: 10381-9.
• Libby, B., Reinholdt, L., and Schimenti, J. (2003) Positional cloning and characterization of Mei1, a novel, vertebrate-specific gene required for normal meiotic chromosome synapsis in mice. PNAS, 100: 15706-15711.
• Ward, J., Reinholdt, L., Hartford, S., Wilson, L., Munroe, R., Schimenti, K., Libby, B., O’Brien, M., Pendola, J., Eppig, J. and Schimenti, J. (2003) Towards the genetics of mammalian reproduction: induction and mapping of gametogenesis mutants in mice. Biology of Reproduction, 69, 1615-25.
• Shima, N., Hartford, S., Duffy, T., Wilson, L., Schimenti, K. and Schimenti, J. (2003) Phenotype based identification of mouse chromosome instability mutants. Genetics, 163:1031-1040.