ERC FUNDED PROJECTS

One of the most astonishing processes in the life of a cell is the division into two daughter cells. Such a highly organized process would presumably be regulated tightly by the underlying centromeric DNA sequence; however, the sites of chromosome attachment to the microtubule spindle are regulated by epigenetic mechanisms. The best-characterized epigenetic mark for centromeres is the histone H3-variant CENP-A, which replaces H3 in some of the nucleosomes within centromeric chromatin. Centromeres are embedded in pericentromeric heterochromatin and it has become apparent in recent years that heterochromatin is transcribed into non-coding RNAs. We have recently shown that a long non-coding RNA from pericentromeric heterochromatin of the X chromosome (SATIII) in Drosophila melanogaster localizes in trans to centromeres of all other chromosomes and is an essential component for correct loading and maintenance of CENP-A and, therefore, genome stability. Additional RNAs in Drosophila and RNAs from other species have been linked to centromeric chromatin, but their function is not understood. We propose that a complex, RNA-based epigenetic mechanism regulates centromere establishment and function. This proposal is designed to the precise function of SATIII RNA by identifying the associated protein complexes as well as structural and post-transcriptional features of SATIII. We will evaluate the mechanisms by which SATIII functions as a heritable mark of centromeres through generations, during the developing germ line, and species separation. In parallel, we will systematically identify and characterize centromere-associated RNAs (cenRNAs) in Drosophila and human cells. We will elucidate their function in centromere biology and chromosome segregation, essentially as we have done and propose to do for SATIII. These experiments are designed to provide a detailed understanding of the essential, RNA-based epigenetic regulation of centromeres.

1 896 250 €

Start date: 2016-07-01, End date: 2021-06-30

"DNA in higher organisms is organized in a nucleoprotein complex called chromatin. The structure of chromatin is responsible for compacting DNA to fit within the nucleus and for governing its access in nuclear processes. Epigenetic information is encoded chiefly via chromatin modifications. Readout of the genetic code depends on chromatin remodeling, a process actively altering chromatin structure. An understanding of the hierarchical structure of chromatin and of structurally based, remodeling mechanisms will have enormous impact for developments in medicine. Following our high resolution structure of the nucleosome core particle, the fundamental repeating unit of chromatin, we have endeavored to determine the structure of the chromatin fiber. We showed with our X-ray structure of a tetranucleosome how nucleosomes could be organized in the fiber. Further progress has been limited by structural polymorphism and crystal disorder, but new evidence on the in vivo spacing of nucleosomes in chromatin should stimulate more advances. Part A of this application describes how we would apply these new findings to our cryo-electron microscopy study of the chromatin fiber and to our crystallographic study of a tetranucleosome containing linker histone. Recently, my laboratory succeeded in providing the first structurally based mechanism for nucleosome spacing by a chromatin remodeling factor. We combined the X-ray structure of ISW1a(ATPase) bound to DNA with cryo-EM structures of the factor bound to two different nucleosomes to build a model showing how this remodeler uses a dinucleosome, not a mononucleosome, as its substrate. Our results from a functional assay using ISW1a further justified this model. Part B of this application describes how we would proceed to the relevant cryo-EM and X-ray structures incorporating dinucleosomes. Our recombinant ISW1a allows us to study in addition the interaction of the ATPase domain with nucleosome substrates."

2 500 000 €

Start date: 2013-01-01, End date: 2017-12-31

The interest on autophagy, an evolutionarily conserved process in eukaryotes, has enormously increased in the last years, since autophagy is involved in many diseases such as cancer and neurodegenerative disorders. Autophagosome formation is the key process in autophagy. Despite extensive work, the model of autophagosome formation is not yet well established. Some important questions on autophagosome biogenesis remain to be elusive, such as where the bona fide marker protein of autophagosome, LC3, is lipidated, how lipidated LC3 functions in autophagosome formation, and how the proteins for LC3 lipidation and delipidation are involved in autophagosome formation. Although genetic approaches have been useful to identify genes involved in autophagy, they are chronic and thereby the dynamics of phenotypic change cannot be followed, making them not suited for study highly dynamic process such as autophagosome formation. Herein, I propose to develop and use novel chemical probes to address these issues. First, I plan to prepare semi-synthetic caged LC3 proteins and apply them to monitor dynamics of autophagosome formation in the cell in order to address those questions on autophagosome formation. The semi-synthetic LC3 proteins are expected to confer a temporal control and to realize manipulation of protein structure, which renders such studies possible. Second, I intend to develop a versatile approach targeting specific endogenous proteins using a reversible chemically induced dimerization (CID) system, termed as “knock on and off” strategy. I plan to use this approach to elucidate the function of two distinct PI3K complexes in autophagosome formation. On one hand, the establishment of novel approaches will open up a new avenue for studying biological processes. On the other hand, the use of the tool will reveal the mechanism of autophagy.

1 500 000 €

Start date: 2016-09-01, End date: 2021-08-31

A central question in chromatin biology is how to organize the genome and mark specific regions with histone variants. Understanding how to establish and maintain, but also change chromatin states is a fundamental challenge. Histone chaperones, escort factors that regulate the supply, loading, and degradation of histone variants, are key in their placement at specific chromatin landmarks and bridge organization from nucleosomes to higher order structures. A series of studies have underlined chaperone-variant partner selectivity in multicellular organisms, yet recently, dosage imbalances in natural and pathological contexts highlight plasticity in these interactions. Considering known changes in histone dosage during development, one should evaluate chaperone function not as fixed modules, but as a dynamic circuitry that adapts to cellular needs during the cell cycle, replication and repair, differentiation, development and pathology. Here we propose to decipher the mechanisms enabling adaptability to natural and experimentally induced changes in the dosage of histone chaperones and variants over time. To follow new and old proteins, and control dosage, we will engineer cellular and animal models and exploit quantitative readout methods using mass spectrometry, imaging, and single-cell approaches. We will evaluate with an unprecedented level of detail the impact on i) soluble histone complexes and ii) specific chromatin landmarks (centromere, telomeres, heterochromatin and regulatory elements) and their crosstalk. We will apply this to determine the impact of these parameters during distinct developmental transitions, such as ES cell differentiation and T cell commitment in mice. We aim to define general principles for variants in nuclear organization and dynamic changes during the cell cycle/repair and in differentiation and unravel locus specific-roles of chaperones as architects and bricklayers of the genome, in designing and building specific nuclear domains.

2 499 697 €

Start date: 2016-07-01, End date: 2022-06-30