ERC FUNDED PROJECTS

The mechanism of cell division is conserved in many eukaryotes, from yeast to man. A contractile ring of filamentous actin and myosin II motors generates the force to bisect a mother cell into two daughters. The actomyosin ring is among the most complex cellular machines, comprising over 150 proteins. Understanding how these proteins organize themselves into a functional ring with appropriate contractile properties remains one of the great challenges in cell biology. Efforts to generate a comprehensive understanding of the mechanism of actomyosin ring assembly have been hampered by the lack of structural information on the arrangement of actin, myosin II, and actin modulators in the ring in its native state. Fundamental questions such as how actin filaments are assembled and organized into a ring remain actively debated. This project will investigate key issues pertaining to cytokinesis in the fission yeast Schizosaccharomyces pombe, which divides employing an actomyosin based contractile ring, using the methods of genetics, biochemistry, cellular imaging, DNA origami, genetic code expansion, and click chemistry. Specifically, we will (1) attempt to visualize actin filament assembly in live cells expressing fluorescent actin generated through synthetic biological approaches, including genetic code expansion and click chemistry (2) decipher actin filament polarity in the actomyosin ring using total internal reflection fluorescence microscopy of labelled dimeric and multimeric myosins V and VI generated through DNA origami approaches (3) address when, where, and how actin filaments for cytokinesis are assembled and organized into a ring and (4) reconstitute actin filament and functional actomyosin ring assembly in permeabilized spheroplasts and in supported bilayers. Success in the project will provide major insight into the mechanism of actomyosin ring assembly and illuminate principles behind cytoskeletal self-organization.

2 863 705 €

Start date: 2015-11-01, End date: 2020-10-31

Imagine being able to design into living cells and organisms de novo vesicle transport mechanisms that do not naturally exist? At one level this is a wild-eyed notion of synthetic biology. But we contend that this vision can be approached even today, focusing first on the process of exocytosis, a fundamental process that impacts almost every area of physiology. Enough has now been learned about the natural core machinery (as recognized by the award of the 2013 Nobel Prize in Physiology or Medicine to the PI and others) to take highly innovative physics/engineering- and DNA-based approaches to design synthetic versions of the secretory apparatus that could someday open new avenues in genetic medicine. The central idea is to introduce DNA-based functional equivalents of the core protein machinery that naturally form (coats), target (tethers), and fuse (SNAREs) vesicles. We have already taken first steps by using DNA origami-based templates to produce synthetic phospholipid vesicles and complementary DNA-based tethers to specifically capture these DNA-templated vesicles on targeted bilayers. Others have linked DNA oligonucleotides to trigger vesicle fusion. The next and much more challenging step is to introduce such processes into living cells. We hope to break this barrier, and in the process start a new field of research into “synthetic exocytosis”, by introducing Peptide-Nucleic Acids (PNAs) of tethers and SNAREs to re-direct naturally-produced secretory vesicles to artificially-programmed targets and provide artificially-programmed regulation. PNAs are chosen mainly because they lack the negatively charged phosphate backbones of DNA, and therefore are more readily delivered into the cell across the plasma membrane. Future steps, would include producing the transport vesicles synthetically within the cell by externally supplied origami-based PNA or similar cages, and - much more speculatively - ultimately using encoded DNA and RNAs to provide these functions.

3 000 000 €

Start date: 2015-09-01, End date: 2021-08-31

ATM is the protein kinase that is mutated in the hereditary autosomal recessive disease ataxia telangiectasia (A-T). A-T patients display immune deficiencies, cancer predisposition and radiosensitivity. The molecular role of ATM is to respond to DNA damage by phosphorylating its substrates, thereby promoting repair of damage or arresting the cell cycle. Following the induction of double-strand breaks (DSBs), the NBS1 protein is required for activation of ATM. But ATM can also be activated in the absence of DNA damage. Treatment of cultured cells with hypotonic stress leads to the activation of ATM, presumably due to changes in chromatin structure. We have recently described a second ATM cofactor, ATMIN (ATM INteractor). ATMIN is dispensable for DSBs-induced ATM signalling, but ATM activation following hypotonic stress is mediated by ATMIN. While the biological role of ATM activation by DSBs and NBS1 is well established, the significance, if any, of ATM activation by ATMIN and changes in chromatin was up to now completely enigmatic. ATM is required for class switch recombination (CSR) and the suppression of translocations in B cells. In order to determine whether ATMIN is required for any of the physiological functions of ATM, we generated a conditional knock-out mouse model for ATMIN. ATM signaling was dramatically reduced following osmotic stress in ATMIN-mutant B cells. ATMIN deficiency led to impaired CSR, and consequently ATMIN-mutant mice developed B cell lymphomas. Thus ablation of ATMIN resulted in a severe defect in ATM function. Our data strongly argue for the existence of a second NBS1-independent mode of ATM activation that is physiologically relevant. While a large amount of scientific effort has gone into characterising ATM signaling triggered by DSBs, essentially nothing is known about NBS1-independent ATM signaling. The experiments outlined in this proposal have the aim to identify and understand the molecular pathway of ATMIN-dependent ATM signaling.

1 499 881 €

Start date: 2012-02-01, End date: 2018-01-31

During an organism’s development it must integrate internal and external information. An example in plants, whose development stretches across their lifetime, is the coordination between environmental stimuli and endogenous cues on regulating the key hormone gibberellin (GA). The present challenge is to understand how these diverse signals influence GA levels and how GA signalling leads to diverse GA responses. This challenge is deepened by a fundamental problem in hormone research: the specific responses directed by a given hormone often depend on the cell-type, timing, and amount of hormone accumulation, but hormone concentrations are most often assessed at the organism or tissue level. Our approach, based on a novel optogenetic biosensor, GA Perception Sensor 1 (GPS1), brings the goal of high-resolution quantification of GA in vivo within reach. In plants expressing GPS1, we observe gradients of GA in elongating root and shoot tissues. We now aim to understand how a series of independently tunable enzymatic and transport activities combine to articulate the GA gradients that we observe. We further aim to discover the mechanisms by which endogenous and environmental signals regulate these GA enzymes and transporters. Finally, we aim to understand how one of these signals, light, regulates GA patterns to influence dynamic cell growth and organ behavior. Our overarching goal is a systems level understanding of the signal integration upstream and growth programming downstream of GA. The groundbreaking aspect of this proposal is our focus at the cellular level, and we are uniquely positioned to carry out our multidisciplinary aims involving biosensor engineering, innovative imaging, and multiscale modelling. We anticipate that the discoveries stemming from this project will provide the detailed understanding necessary to make strategic interventions into GA dynamic patterning in crop plants for specific improvements in growth, development, and environmental responses.

1 499 616 €

Start date: 2018-01-01, End date: 2022-12-31