Research TopicsDepartment of Cell and Structural Biology
Ph.D. (1997) Emory University
Research Topics
- Gene Regulation
- Transcription Repression
- Chromatin Structure
Research Interests
My laboratory is interested in the establishment and maintenance of transcriptional repression, focusing on the role of chromatin structure. Using a combination of experimental approaches including conventional chromatography, biochemistry, and molecular biology, we are purifying and characterizing novel chromatin remodeling machine involved in targeted transcriptional repression. We use the early development of the African clawed frog, Xenopus laevis, as a biochemical tool as well as a model developmental system to dissect in vivo function and targeting of the co-repressor complexes.
In a eukaryotic cell, DNA is wrapped around the core histone proteins and is in contact with many additional proteins. This DNA/protein complex is chromatin. The chromatin is further packaged into more complex and compact higher order chromatin structures. This type of structure is necessary as a typical eukaryotic cell needs to package up to 2 meters of DNA into a nucleus of around 10 microns. However, while organizing and compacting the DNA, the chromatin structure creates a formidable barrier to such molecular processes as transcription, replication, and recombination, requiring the chromatin structure to be dynamic. Recent discoveries have revealed that cells contain large multi-subunit protein complexes capable of modifying the chromatin proteins. Targeting of these complexes results in a localized chromatin structure that is either more amenable to molecular processes or more refractory to molecular processes. We are interested in complexes that are involved in the establishment and/or maintenance of a transcriptionally repressive chromatin environment. The two projects in the laboratory focus on (1) DNA methylation-dependent transcription repression, and (2) nuclear hormone receptor-mediated transcription repression. The projects are similar in that specific DNA binding proteins recruit the transcriptional co-repressor proteins and histone deacetylases to alter the local chromatin environment. They are different at the level of the repression that is established. Methylation-dependent repression is very stable and virtually never will be reversed to an activated state under normal cellular conditions. N-CoR-mediated repression is readily reversible upon an activation signal. Studying the two systems, we will get a better understanding of how a repressive chromatin environment is established and maintained.
Currently we are biochemically purifying several protein complexes that contain methyl-DNA binding domain (MBD) proteins, DNA methyltransferase activity, or nuclear hormone receptor co-repressors from X, laevis egg and oocyte extracts. Of particular interest are the complexes that also contain his tone deacetylase activity. We then identify the in vivo targets of these complexes and disseminate the mechanisms of differential targeting. In addition, both in vivo and in vitro chromatin assembly systems are utilized to understand how to set up a repressive chromatin environment. In the near future, the external development of X. laevis and X. tropicalis will be exploited using transgenesis techniques to assess complex function in early development.
Key Words Xenopus laevis, DNA methylation, Nuclear hormone
receptor, Corepressor complexes, Chromatography, Histone modification, Chromatin