Dissecting the functions of the novel factors Pdp3 and Lem2 in heterochromatin regulation

• Applicant: Professor Dr. Sigurd Braun
• Subject Area: General Genetics and Functional Genome Biology ; Biochemistry ; Evolutionary Cell and Developmental Biology (Zoology)
• Term: from 2014 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 260011276

The genome of eukaryotic cells is organized into distinct chromatin domains. The functional partitioning into transcriptionally active (euchromatin) and silent domains (heterochromatin) is crucial for diverse cellular functions and genome stability. It allows also the timely gene expression during development. Furthermore, silent chromatin differs topologically from active chromatin and is localized in many model systems at the nuclear periphery. This differentiation of eu- and heterochromatin is reversible and largely independent of the underlying DNA sequence, yet the acquired chromatin states are fairly stable and can be inherited (epigenetics). Significant advances have been made in identifying enzymatic activities and structural components that are involved in establishing epigenetic marks on chromatin. However, the regulatory mechanisms that coordinate these factors are still poorly understood. Recently, we have isolated through unbiased genetic screens in the model organism fission yeast (Schizosaccharomyces pombe) several new candidates that affect heterochromatic silencing and potentially control the spatial distribution of chromatin-associated factors within heterochromatin and its localization to the nuclear periphery. In this proposal, we will focus on deciphering the specific roles of two novel factors in heterochromatin regulation: Pdp3 and Lem2. Pdp3 contains a putative methyl-binding PWWP domain and is part of a histone acetyltransferase (HAT) complex. Our unpublished data suggest that Pdp3 contributes to silencing by controlling the activity of the HAT. We will test whether Pdp3 discriminates between different chromatin regions through its PWWP domain and thereby regulates the spatial distribution of the HAT complex on chromatin. The nuclear envelope protein Lem2 is a homolog of metazoan lamin-associated proteins. We found that Lem2 contributes to silencing of various heterochromatic domains and acts redundantly with other peripheral factors. We will therefore test the hypothesis whether Lem2 promotes silencing through anchoring heterochromatin to the nuclear periphery and examine how Lem2 mediates the bridging of silent chromatin to the nuclear envelope. We will perform these studies in the powerful fission yeast model that harbors essential hallmarks of metazoan heterochromatin and is ideally suited for applying functional genetics, high-throughput studies, and genome-wide analysis. Together, these efforts will provide profound mechanistic insights into how heterochromatin is controlled and coordinated in fission yeast. While such molecular mechanisms are difficult to study in multicellular systems, they may reflect basic principles that due to the strong conservation of heterochromatin can likely be transferred also to metazoans and humans.

• DFG Programme: Research Grants