Chromatin- and Epigenetics Laboratory
Structure & Function of Chromatin: Filamentous Fungi
Histone methylation in filamentous fungi
(principal investigator: Gerald Brosch)
DNA of the eukaryotic nucleus is organized by histones, small basic proteins which are subject to reversible, postsynthetic modifications, such as phosphorylation, acetylation and methylation. During the past years it became evident that a complex interplay between these modifications occurring on the histone tails exist which are all involved in gene-specific regulation.
Histone methylation is carried out by histone methyltransferases (HMTs) which are classified due to their substrate specificity. Whereas protein arginine methyltransferases (PRMTs) can use arginine residues on H3 and H4 as substrate, SET domain containing HMTs catalyse the methylation of lysines on the same histone molecules. The recent identification and analysis of different HMTs revealed enzymes that stimulate either gene repression or gene activation, depending on the residue being modified and the type of methylation being introduced.
The long-term objective of our research is to investigate the functional role of protein methylation in filamentous fungi. We are performing our studies in the model organism A. nidulans since this fungus is not only well suited to study general mechanisms of chromatin regulation, but, in addition allows to explore the significance of chromatin modifications for fungal virulence (e.g. aspergillosis) and secondary metabolism (e.g. production of antibiotics, immunosuppressants, toxins).
We have identified three distinct PRMTs which all exhibit histone methyltransferase activity in vitro and in vivo. One of these proteins, termed RmtB, has an exceptional position because it displays both enzymatic and structural properties that are different from other known PRMTs. To study the functional role of PRMTs in A. nidulans we are currently deleting the corresponding PRMT genes by targeted gene replacement and are analysing putative growth defects of rmtA/ rmtB, and rmtC deletion mutants under various growth conditions. These studies will be completed by the generation of double and triple mutant strains and the concomitant investigation of physiological and developmental effects. Finally, the analysis of global gene expression patterns, the study of effects of rmtA, rmtB, and rmtC deletion on the regulation of genes involved in secondary metabolism pathways, and the identification of novel substrate proteins of PRMTs will help to clarify the role of arginine methylation in Aspergillus.
Functional roles of distinct histone deacetylases in the filamentos fungus Aspergillus nidulans
(principal investigator: Stefan Grässle, supported by the Austrian Science Foundation (FWF), Project P-15439-BIO, P-19750-BIO, P24803-B20-BIO)
Histone acetylation plays a crucial role in the processes of gene regulation in eukaryots. In particular, histones can be acetylated by histone acetyltransferases (HATs) and can be deacetylated by a second group of enzymes, the histone deacetylases (HDACs). In contrast to HATs, for which to date no potent inhibitors are known, there is a panel of structurally unrelated agents available that affect HDACs in a very selective way. Today these inhibitors are important tools for the study of histone acetylation processes. Our working group has sound expertise in the the study of histone acetylation/deacetylation processes and in brief in the purification of HATs and HDACs of multiple organisms. Recently, we have identified and partially characterized HDACs of different classes in the filamentous fungus Aspergillus nidulans. The further characterization and the clarification of the function of these enzymes within our model organism is the goal of this project. Since filamentous fungi are more complex than yeast in many important aspects yet genetic manipulation is relatively simple and easy to perform, they have widely been regarded as model systems to study the basis of eukaryotic gene regulation. Moreover, many of these organisms contribute to the decay of organic material and thereby play an important role in the spoilage of food. But there are also filamentous fungi which represent dangerous pathogenic agents for people such as the closely related species to A. nidulans, A. fumigatus, which can cause life-threatening infections in patients that have a compromized immune system. For these reasons the study of these group of organisms is also from a large economic and medical interest.