DNA associates with an octamer of histone proteins in the nucleus of eukaryotic cells to form the nucleosome, which serves as the building block for higher-order chromatin structures. We study the role of chromatin and chromatin-modifying proteins in regulating gene expression, genome integrity and other essential cellular processes. A variety of model systems are used, including yeast (Saccharomyces cerevisiae), mice, embryonic stem (ES) cells and various tissue culture cell lines.
We use genetic and biochemical approaches to define the functions of the Set1 methyltransferase and have discovered unexpected functions for this enzyme in the regulation of mitosis. This work has also identified novel nodes of regulatory cross-talk between post-translational modifications in histone and non-histone proteins.
Set1 is the sole lysine methyltransferase that methylates histone H3 on lysine residue 4 in yeast. We discovered that Set1 also mediates methylation of the kinetochore protein Dam1. Cell. 2011. 146(5):709-19.
Set1 mutants display a thick mitotic spindle phenotype. Tubulin is shown in green, DAPI, which stains nuceic acid (DNA) is shown in blue. The white dotted lines outline mitotic yeast cells. Genes Dev. 2016. 30(10):1187-97.
Mouse Models and Embryonic Stem Cells
In mice, research includes gene targeting and transgenic approaches to understand the functions of histone acetyltransferases (GCN5 and PCAF) and deubiquitinases (USP22, USP27X) during mouse development and in adult tissues. Our overall goal is to understand the importance of chromatin remodeling and epigenetics in normal cell growth and development. We then hope to gain insights into how misregulation of these activities contributes to disease states, including various cancers.
In collaboration with Dr. Jeff Wrana at the Lunenfeld-Tanenbaum Research Institute, we have shown that Myc drives expression of the SAGA component Gcn5. Together, Myc and Gcn5, a histone acetyltransferase, reprogram fibroblasts to a stem cell state by activating an alternative splicing network. This collaboration also led to the finding that Gcn5 is important for Myc-mediated stem cell self-renewal in embryonic stem cells. These findings raise the possibility that Myc-Gcn5 could also work together to promote tumor formation. Genes Dev. 2015 Jun 15;29(12):1341
The image shows an immunofluoresence microscopy image of a day 5 embryoid body (EB) differentiated from mouse ES cells. We use EBs to dissect the functions of SAGA (GCN5) during stem cell differentiation.
Cell and Tissue Culture
Many of our projects also use mammalian cell culture techniques either as the primary model for experiments or to supplement other findings in yeast or mice. Working with these cell lines involves transfection, siRNA, chromatin immunoprecipitation and biochemical approaches to define the functions and mechanisms of regulation of histone-modifying enzymes.
We have identified two histone H2B deubiquitinating enzymes important for tumor growth. We identified USP51 and USP27X as close homologs of USP22, which is overexpressed in highly aggressive cancers. Further, we demonstrated that ATXN7L3 and ENY2 act as master regulators of USP51 and USP27X to regulate both cell proliferation and xenograft tumor growth. Mol Cell. 2016. 62(4):558-71.