Marc Meneghini, PhD
Medical Sciences Building, #4379
1 King's College Circle
Toronto, ON M5S 1A8
marc.meneghini@utoronto.ca

Epigenetic regulation in yeast and during animal development

My research uses the nematode C. elegans and the unicellular yeast S. cerevisae as model systems to study mechanisms controlling entry into, maintenance of, and exit from quiescent stages. A defining characteristic of quiescence is disengagement from the cell cycle and entry into an alternative cell cycle phase called "G0". As defects in the maintenance of G0 are a frequent cause of oncogenesis in humans, it is of great interest to understand the fundamental mechanisms governing quiescence. During animal development, terminal differentiation of cells is often coordinated with entry into G0. Because differing cell types express discrete information encoded in their genomes, epigenetic mechanisms must function in these cells to regulate genome utilization. Epigenetic regulation of gene expression is mediated by chromatin, the complex of DNA with its associated histones and chemical modifications. Post-translational modifications to histone proteins such as methylation and acetylation and substitution of canonical histones with variant forms impart much epigenetic information to chromatin. The lab's studies have an emphasis on epigenetic regulation of gene expression during these developmental biologies.

During C. elegans embryonic development, the primordial germline stem cell (PGC) enters a quiescent stage and survival of the PGC during this quiescent stage requires a specific epigenetic program. We have determined previously that the yeast histone H2A variant, H2A.Z, functions to specify chromatin state and have extended this work to include an analysis of the single C. elegans H2A.Z homolog. Intriguingly, the data indicate that PGC survival is dependent on H2A.Z function. Thus, like in yeast, H2A.Z may function in metazoans to regulate chromatin state.

As with C. elegans, but not as appreciated per se, the life cycle of S. cerevisiae includes a differentiation program that produces specialized quiescent cells. In yeast these quiescent cells are the products of meiotic division of diploids, which then differentiate to produce exceptionally long-lived spores. Upon exposure to the proper nutritional cues, these spores can germinate, exiting from the spore G0-like state and re-enter the cell cycle as haploids. We have recently discovered that global demethylation of the lysine-4 residue of histone H3 (H3MeK4) occurs as yeast cells enter quiescence during sporogenesis and this global demethylation requires a gene called JHD2. JHD2 is the yeast orthologue of human Rbp2 (Retinoblastoma binding protein 2), a recently confirmed histone demethylase. In addition to its demethylation defect, using genome-wide microarray experiments we found jhd2 mutants exhibit reduced gene induction during sporogenesis. As the tumor suppressor Rb protein regulates entry and exit from quiescence in humans, and there is growing evidence that Rbp2 participates in this process, the parallels between Jhd2 function and Rbp2 function are intriguing. Extending these findings concerning JHD2 is a focus in the lab.

Using genetic, genomic, molecular and cellular approaches, the lab pursues two broad aims.

1. Functional genomic characterization of sporogenesis and germination in S. cerevisiae.
2. Advancing the hypothesis that histone variant H2A.Z functions in quiescent animal cells to regulate epigenetic state.

Recent Publications

Raisener, R.M., Hartley, P.D., Meneghini, M.D., Bao, M.Z., Liu, C.L., Schreiber, S.L., Rando, O.J., and Madhani, H.D. (2005). Histone variant H2A.Z marks the 5' end of both active and inactive genes in euchromatin. Cell. 123(2): 233-248.

Kobor, M.S., Venkatasubrahmanyam, S., Meneghini, M.D., Gin, J.G., Jennings, J.L., Link, A.J., Madhani, H.D., and Rine, J. (2004). Swr1p, a conserved member of the ATP-dependent chromatin remodeling enzyme family, forms a multisubunit complex with histone variant H2A.Z and mediates its deposition into euchromatic nucleosomes. PLoS Biol. 2(5): E131.

Meneghini, M.D., Wu, M., and Madhani , H. D. (2003). Conserved histone variant H2A.Z protects euchromatin from the ectopic spread of silent heterochromatin. Cell. 112(5): 725-736.

Maduro, M.F., Meneghini, M.D., Bowerman, B., Broitman-Maduro, G., and Rothman, J.H. (2001). Restriction of mesendoderm to a single blastomere by the combined action of SKN-1 and a GSK-3ß homolog is mediated by MED-1 and -2 in C. elegans. Molecular Cell. 7(3): 475-485.

Schlesinger, A., Shelton, C.A., Maloof, J.N., Meneghini, M., and Bowerman, B. (2000). Wnt pathway components orient a mitotic spindle in the early Caenorhabditis elegans embryo without requiring transcription in the responding cell. Genes & Dev. 13: 2028-2038.

Meneghini, M.D., Ishitani, T., Carter, J.C., Hisamoto, N., Ninomiya-Tsuji, J., Thorpe, C.J., Hamill, D.R., Matsumoto, K., and Bowerman, B. (1999). MAP kinase and Wnt pathways converge to downregulate an HMG-domain repressor in Caenorhabditis elegans. Nature, 399:

Ishitani, T., Ninomiya-Tsuji, J., Nagai, S., Nishita, M., Meneghini, M., Barker, N., Waterman, M., Bowerman, B., Clevers, H., Shibuya, H., and Matsumoto, K. (1999). The TAK1-NLK-MAPK-related pathway antagonizes signalling between ß-catenin and transcription factor TCF. Nature, 399: 798-802

Keesee, S.K., Meneghini, M.D., Szaro, R.P., and Wu, Y.J. (1994). Nuclear matrix proteins in human colon cancer. Proc. Natl. Acad. Sci. U.S.A. 91: 1913-1916.

Miller, T., Beausang, L.A., Meneghini, M., and Lidgard, G. (1993). Death-induced changes to the nuclear matrix: the use of anti-nuclear matrix antibodies to study agents of apoptosis. Biotechniques, 15: 1042-1047.