Ó Copyright Kusch Lab 2006-08 - Ò All rights reserved
The epigenetics of developmental gene expression and genome stability
Chromatin structure bears important epigenetic information to ensure proper gene regulation and the faithful transmission of the genetic information during cell divisions. Preliminary studies support that certain chromatin restructuring events do not only occur during gene regulation, but also at sites of DNA repair, replication and recombination. Research in our laboratory focuses on the complexes that regulate such processes and how they function. We believe that these complexes catalyze fundamental reactions that are directly involved in the reversible 'opening' and 'closing' of chromatin at sites of transcription, DNA replication or repair.
We take a broad array of approaches to study the structure and function of these complexes including biochemical, genetic, reverse genetic, proteomic/mass spectrometric, functional genomic, enzymatic, and cell biological methods. The organism of our choice is the fruit fly, Drosophila melanogaster, for its excellence as model for developmental as well as chromatin-related studies. In fact, Drosophila has been the forefront genetic organism for the identification of chromatin modifiers that regulate developmental gene expression. Most importantly, chromatin restructuring complexes from flies and humans appear to be structurally and functionally extremely well conserved. We therefore expect our findings to unravel the molecular etiology of certain cancers and to lead to the development of new anticancer therapeutics.
Histone H2Av-exchanging complexes
We previously have characterized the dTip60 multiprotein complex, which contains various tumor suppressors including the H2Av histone variant. H2Av plays key roles in developmental gene regulation as well as DNA double strand break repair, and therefore is of our particular interest. Phosphorylation of H2Av-relatives is a universal DNA double strand marker from yeast to humans. Using in vivo studies in embryos and in vitro histone exchange systems, we were able to demonstrate that the dTip60 complex catalyzes the exchange of phospho-H2Av with unmodified H2Av during DNA repair.
In fact, the dTip60 complex contains several histone code readers and writers. Our goal is to better understand the contribution of these subunit to function of the dTip60 complex in both chromatin repair as well as developmental gene regulation. Besides the dTip60 complex, we have identified at least two more complexes that target H2Av. These complexes also contain multiple readers and writers of chromatin structure. We currently are investigating their function and their relationship to the dTip60 complex.
The role of MYST-type acetyltransferases in development and DNA repair
Tip60 is one of the prototypic members of the MYST-type histone acetyltransferase family. Other members of this enzyme family function in hematopoietic stem cell differentiation and other developmental processes, cancer progression, chromosome stability, DNA repair, replication, and recombination. Our preliminary data support strong similarities in structure and function between these MYST-type acetyltransferase-containing complexes in humans and flies. Our goal is to dissect structure and function of all MYST-type histone acetyltransferase-containing complexes from flies with particular emphasis on genome integrity and developmental gene expression. Intriguingly, multiple subunits of these complexes contain domains with affinity to hypermethylated nucleosomes, and we expect these complexes to closely interact with metabolizers of methylated histones.
The Methyl/Acetyl-link
We have identified several enzyme complexes with transcription-related chromatin remodeling activity. All functionally interact with MYST-type acetyltransferases. Indeed, there are strong functional links between histone methylation and acetylation events. Not surprisingly, our preliminary studies indicated that complexes involved in the turnover of these marks share structural and functional similarities. We currently study their precise function and interactions both in vitro and in vivo.
