ERC FUNDED PROJECTS

Fault-tolerant topological quantum computation has become one of the most exciting research directions in modern condensed matter physics. As a key operation the braiding of non-Abelian anyons has been proposed theoretically. Such exotic quasiparticles can be realized as zero-energy Majorana bound states at the ends of one-dimensional magnetic nanowires in proximity to s-wave superconductors in the presence of high spin-orbit coupling. In contrast to previous attempts to realize such systems experimentally, based on the growth of semiconducting nanowires or the self-assembly of ferromagnetic nanowires on s-wave superconductors, we propose to design Majorana bound states in artificially constructed single-atom chains with non-collinear spin-textures on elemental superconducting substrates using scanning tunnelling microscope (STM)-based atom manipulation techniques. We would like to study at the atomic level the formation of Shiba bands as a result of hybridization of individual Shiba impurity states as well as the emergence of zero-energy Majorana bound states as a function of chain structure, length, and composition. Moreover, we will construct model-type platforms, such as T-junctions, rings, and more complex network structures with atomic-scale precision as a basis for demonstrating the manipulation and braiding of Majorana bound states. We will make use of sophisticated experimental techniques, such as spin-resolved scanning tunnelling spectroscopy (STS) at micro-eV energy resolution, scanning Josephson tunnelling spectroscopy, and multi-probe STS under well-defined ultra-high vacuum conditions, in order to directly probe the nature of the magnetic state of the atomic wires, the spin-polarization of the emergent Majorana states, as well as the spatial nature of the superconducting order parameter in real space. Finally, we will try to directly probe the quantum exchange statistics of non-Abelian anyons in these atomically precise fabricated model-type systems.

2 499 750 €

Start date: 2019-01-01, End date: 2023-12-31

Self-propelling, i.e., active colloidal particles constitute a novel class of non-equilibrium systems which exhibit structural and dynamical features similar to those in assemblies of bacteria or other motile organisms. Due to their reduced complexity, they provide an intriguing chance to understand the formation of dynamical structures in non-equilibrium systems in unprecedented detail. A central question in this rapidly growing field is, how interaction-rules determine the creation of e.g. swarms or complex networks. In addition to ordinary inter particle and hydrodynamic forces, interaction-rules can be much more complex. For example, they can regulate the particle motility depending on their relative orientation, their local density or otherwise distinct particle configurations. Here, we propose an experimental approach which aims towards controlling the amplitude and direction of the particle’s motility in dense active suspensions on a single particle level. Particle-propulsion is achieved by a light-activated diffusiophoretic mechanism, where the particle motility is controlled by an incident light field. By means of an acoustic-optical modulator and a feed-back loop, we create dynamical and spatially-resolved light fields which depend on the current configuration of active particles and user-defined interaction rules. Because these rules are imposed externally and not by internal forces, this permits the experimental realization of a wide range of rules (linear, non-linear, and even non-reciprocal) in dense, two-dimensional active systems. We expect, that the experimental realization of user-defined interaction-rules largely extends our understanding how active matter can organize in dynamical structures. In addition, the perspective of enhanced control of active particles, as suggested within this proposal, will be of considerable importance for their use as autonomous micro robots which will deliver payloads in liquid environments.

2 036 750 €

Start date: 2016-10-01, End date: 2021-09-30

Neural circuits, composed of interconnected neurons, represent the basic unit of the nervous system. One way to understand the highly complex arrangement of cross-talking, serial and parallel circuits is to resolve its developmental and evolutionary emergence. The rationale of the research proposal presented here is to elucidate the complex circuitry of the vertebrate and insect forebrain by comparison to the much simpler and evolutionary ancient “connectome” of the marine annelid Platynereis dumerilii. We will build a unique resource, the Platynereis Neuron Type Atlas, combining, for the first time, neuronal morphologies, axonal projections, cellular expression profiling and developmental lineage for an entire bilaterian brain. We will focus on five days old larvae when most adult neuron types are already present in small number and large part of the axonal scaffold in place. Building on the Neuron Type Atlas, the second part of the proposal envisages the functional dissection of the Platynereis chemosensory-motor forebrain circuits. A newly developed microfluidics behavioural assay system, together with a cell-based GPCR screening will identify partaking neurons. Zinc finger nuclease-mediated knockout of circuit-specific transcription factors as identified from the Atlas will reveal circuit-specific gene regulatory networks, downstream effector genes and functional characteristics. Laser ablation of GFP-labeled single neurons and axonal connections will yield further insight into the function of circuit components and subcircuits. Given the ancient nature of the Platynereis brain, this research is expected to reveal a simple, developmental and evolutionary “blueprint” for the olfactory circuits in mice and flies and to shed new light on the evolution of information processing in glomeruli and higher-level integration in sensory-associative brain centres.

2 489 048 €

Start date: 2012-03-01, End date: 2017-02-28

The regulation of cell migration is central in pattern formation, homeostasis and disease. The proposed research is aimed at investigating the molecular basis for cell motility and the associated polarization of the cell. In view of the dynamic nature of these processes, we have chosen to utilize the migration of Primoridal Germ Cells (PGCs) in zebrafish - a model that offers unique experimental advantages for imaging and experimental manipulations. The fact that molecules facilitating the motility of zebrafish PGCs are evolutionary conserved and the finding that the cells are directed by chemokines, molecules that control a wide range of cell trafficking events in vertebrates, make this in vivo study of particular importance. The proposed work involves both the functional analysis of previously identified candidates and the identification of molecules, which have a presently unknown effect on the migration process. For both objectives, we will employ novel experimental schemes. We will examine the role of proteins in achieving functional cell polarity compatible with efficient motility and response to directional cues, using unique techniques and analysis tools in the context of the living organism. The precise function of the identified proteins will be determined by combining mathematical tools aimed at quantitatively gauging the role of the molecules in conferring proper cell shape, biophysical methods aimed at measuring forces, rigidity and cytoplasm flow and determination of the effect on the organization of relevant structures using cryo electron tomography. Together, this approach would provide a non-conventional understanding of cell migration by correlating structural, morphological and dynamic cellular properties with the ability of cells to effectively migrate towards their target.

1 960 600 €

Start date: 2011-06-01, End date: 2017-05-31

The mechanisms regulating neural stem cells and their progression to neurogenesis are important not only to understand brain development and evolution, but also to elicit neurogenesis after brain injury. Our recent findings imply novel chromatin-associated proteins in the regulation of neural stem cell fate and neurogenesis. Therefore this project aims to understand the molecular mechanisms of how these factors regulate neurogenesis in developing and adult mice (Aim1) and implement this knowledge for reprogramming glia into neurons after brain injury (Aim2). This will be pursued in mouse models in vivo (2.1) and with human glial cells derived from patient brain resections in vitro (2.2). It is well known that transcription factors need to alter the chromatin structure to achieve transcriptional regulation, but the factors involved in this regulation in neural stem and progenitor cells are still ill understood. Therefore the molecular function of the novel chromatin interacting protein Trnp1 with essential roles in neural stem cell (NSC) fate and the chromatin conformation mediated at neurogenic target genes by Pax6/Brg1-containing BAF complexes will be addressed in Aim1. Combined with genome-wide approaches to determine changes in chromatin conformation at neurogenic target gene sites this will greatly further our understanding of key roles of chromatin conformation in neural stem cells and neurogenesis. In Aim2 Trnp1 promoting neural stem cells fate and later acting neurogenic transcription factors will be used to improve neuronal reprogramming after stab wound injury in the murine brain in vivo and in patient-derived glial cells in vitro. Together with novel strategies to induce chromatin looping in a sequence-specific manner this project will not only advance our knowledge at the frontier of transcriptional regulation in neurogenesis, but also implement highly innovative approaches to utilize this knowledge for neuronal repair by direct reprogramming.

2 376 560 €

Start date: 2014-02-01, End date: 2019-01-31

Compounds of transition metals with 4d valence electrons (“4d metals”) play eminent roles in many areas of condensed matter physics ranging from unconventional superconductivity to oxide electronics, but fundamental questions about the interplay between the spin-orbit coupling and electronic correlations at the atomic scale remain unanswered. Momentum-resolved spectroscopies of collective electronic excitations yield detailed insight into the magnitude and spatial range of the electronic correlations, and have thus decisively shaped the conceptual understanding of quantum many-body phenomena in 3d-electron systems. We will devise and build a novel resonant inelastic x-ray scattering (RIXS) instrument capable of determining the dispersion relations of electronic collective modes in 4d-metal compounds with full momentum-space coverage, high energy resolution, and monolayer sensitivity. Data from this instrument will yield comprehensive information about the interaction parameters specifying the electronic Hamiltonians of 4d-electron materials, unique insight into the spin-orbital composition of their excited-state wavefunctions, and definitive tests of proposals to realize Kitaev models with spin-liquid states that are potentially relevant in topological quantum computation. The element-specificity of RIXS will also allow us to determine the microscopic exchange interactions in complex materials with both 3d and 4d valence electrons, and its high sensitivity will enable experiments on operational device structures comprising only a few monolayers. We will thus be able to tightly integrate momentum-resolved spectroscopy with state-of-the-art, monolayer-by-monolayer deposition methods of 4d metal-oxide films and heterostructures. The results will fuel a feedback loop comprising synthesis, characterization, and modeling, which will greatly advance our ability to design materials and devices whose functionality derives from the collective organization of electrons.

3 176 850 €

Start date: 2016-01-01, End date: 2020-12-31

Cell division is fundamental for development. In the early mammalian embryo it drives the rapid proliferation of totipotent cells, the basis for forming the fetus. Given its crucial importance, it is surprising that cell division is particularly error-prone at the beginning of mammalian life, resulting in spontaneous abortion or severe developmental retardation, the incidence of which is increasing with age of the mother. Why aneuploidy is so prevalent and how early embryonic development nevertheless achieves robustness is largely unknown. The goal of this project is a comprehensive analysis of cell divisions in the mouse preimplantation embryo to determine the molecular mechanisms underlying aneuploidy and its effects on normal development. Recent technological breakthroughs, including light sheet microscopy and rapid loss-of-function approaches in the mouse embryo will allow us for the first time to tackle the molecular mechanisms of aneuploidy generation and establish the preimplantation mouse embryo as a standard cell biological model system. For that purpose we will develop next generation light sheet microscopy to enable automated chromosome tracking in the whole embryo. Mapping of cell division errors will reveal when, where, and how aneuploidy occurs, what the fate of aneuploid cells is in the embryo, and how this changes with maternal age. We will then perform high resolution functional imaging assays to identify the mitotic pathways responsible for aneuploidy and understand why they do not fully function in early development. Key proteins will be functionally characterised in detail integrating light sheet imaging with single molecule biophysics in embryos from young and aged females to achieve a mechanistic understanding of the unique aspects of cell division underlying embryonic aneuploidy. The achieved knowledge gain will have an important impact for our understanding of mammalian, including human infertility.

2 497 156 €

Start date: 2017-01-01, End date: 2021-12-31

Colour patterns are prominent features of many animals and have important functions in communication such as camouflage, kin recognition and mate selection. Colour patterns are highly variable and evolve rapidly leading to large diversities even within a single genus. As targets for natural as well as sexual selection, they are of high evolutionary significance. The zebrafish (Danio rerio), a vertebrate model organism for the study of development and disease, displays a conspicuous pattern of alternating blue and golden stripes on the body and on the anal- and tailfins. Mutants with spectacularly altered patterns have been analysed, and novel approaches in lineage tracing have provided first insights into the cellular and molecular basis of colour patterning. These studies revealed that the mechanisms at play are novel and of fundamental interest to the biology of pattern formation. Closely related Danio species have very divergent colour patterns in body and fins offering the unique opportunity to study development and evolution of colour patterns in vertebrates building on the thorough analysis of one model species. Our research in zebrafish will explore the basis of direct interactions between chromatophores mediated by channels and junctions. We will investigate the divergent mode of stripe formation in the fins and the molecular influence of the cellular environment on chromatophore interactions. In closely related Danio species, we will investigate the cellular interactions during pattern formation. We will analyse transcriptomes and genome sequences to identify candidate genes providing the molecular basis for pigment pattern diversity. These candidate genes will be tested by creating mutants and exchanging allelic variants using the CRISPR/Cas9 system. The work will lay the foundation to understand not only the genetic basis of variation in colour pattern formation between Danio species, but also the evolution of biodiversity in other vertebrates.

2 250 000 €

Start date: 2016-11-01, End date: 2021-04-30

Cells in intestinal epithelia turn over rapidly due to aging, damage, and toxins produced by the enteric microbiota. Gut homeostasis is maintained by intestinal stem cells (ISCs) that divide to renew the intestinal epithelium, but little is known about how ISC division and differentiation are coordinated with the loss of spent gut epithelial cells. This proposal addresses the mechanisms of dynamic self-renewal in the intestine of Drosophila. Our recent work has outlined a paradigm explaining intestinal homeostasis in Drosophila that could apply also to humans. A new lab is being established in Heidelberg where we wish to extend these studies. Our objectives are to understand: 1) How intestinal stem cell pool sizes are regulated; 2) How the cytokines and growth factors that mediate gut homeostasis are controlled; and 3) How these signals regulate the ISC cell cycle. Established genetic and cell biological methods will be applied, supported by molecular assays (microarrays, qPCR, ChIP/Seq) of gene control. New pathways of ISC control will be discovered via comprehensive genetic screens using transgenic RNAi and gene over-expression. In vitro culture of ISCs will be developed and used for live imaging and molecular analysis of the mechanisms controlling ISC proliferation and differentiation. These studies should elaborate a paradigm explaining intestinal homeostasis in flies that can guide studies in mammals, eventually contributing to the diagnosis and treatment for diseases in which gut homeostasis is disrupted, such as colorectal cancer and inflammatory bowel disease. Because stem cell biology is so highly relevant to wound healing, regeneration, cancer, aging and degenerative disease, this research could impact human health at many levels.

2 682 080 €

Start date: 2011-05-01, End date: 2016-04-30