Research Projects
(longer than one year)
Capillary Forces inside the Cell (current)
Biomolecular condensates (a.k.a protein condensates or membraneless organelles) are liquid-like domains within cells that form through phase separation of key proteins and mRNA. The phase separation process, and subsequent partitioning of cellular constituents towards the condensate or the surrounding liquid, enable these condensates to alter the biochemical landscape of the cell. Consequently, biomolecular condensates have been recognized as important hubs that alter reaction kinetics and/or signalling within the cell. The emergence of two, distinct phases within the cell, however, also postulates the formation of an energetically costly interface. Such interfaces, and the associated surface tension, are the cause of many behaviors that we consider "liquid-like" in our everyday life, such as coalescence and wetting. These phenomena can be collected under the term of "capillary effects" where, broadly speaking, interfacial energies induces flows and forces.
While the surface tension of these condensates is tiny compared to the surface tension of water droplets in air, the surrounding structures of proteins, filaments and membranes are also very soft and mobile. In fact, the cell finds itself at an fascinating length-scale, where small changes in the properties or size of the condensate or the environment can lead to changes in the system behavior: Small condensates may localize and stick to certain cellular structures whereas large condensates may bend filaments and membranes to induce shape changes in the cell.
(A nice review can be found here: https://doi.org/10.1038/s41586-022-05138-6 )
During my PhD with Eric Dufresne at ETH Zurich, I studied the interactions of stress granules, a cytosolic biomolecular condensate, with the filaments of the cytoskeleton. Using novel analysis methods and statistical physics approaches, we have been able to quantify wetting interactions between stress granules and tubulin, the molecular buildingblock of microtubules (the largest cytosolic filament). While the wetting interactions between stress granule and single tubulin proteins are weak and transient, a full microtubule shows significant wetting towards the stress granule leading to mutual deformations of the condensate and the microtubule network.
Filamentous (f-)actin, a thinner cytoskeletal filament with characteristic flow patterns, on the other hand, does not show such pronounced wetting behavior. Instead, f-actin is important for granule motion: Steric interactions between f-actin and stress granules move the condensates along the characteristic f-actin flow towards the center of the cell.
In 2023, I joined the lab of Roland Knorr at Humboldt-Universität zu Berlin, where we aim to understand and quantify capillary phenomena between biomolecular condensates, filaments and lipid membranes. We joined forces with groups from the Charité University Hospital and Oslo University Hospital to understand how capillary forces structure the cell and how such forces affect cell physiology.
Biomolecular condensates (a.k.a protein condensates or membraneless organelles) are liquid-like domains within cells that form through phase separation of key proteins and mRNA. The phase separation process, and subsequent partitioning of cellular constituents towards the condensate or the surrounding liquid, enable these condensates to alter the biochemical landscape of the cell. Consequently, biomolecular condensates have been recognized as important hubs that alter reaction kinetics and/or signalling within the cell. The emergence of two, distinct phases within the cell, however, also postulates the formation of an energetically costly interface. Such interfaces, and the associated surface tension, are the cause of many behaviors that we consider "liquid-like" in our everyday life, such as coalescence and wetting. These phenomena can be collected under the term of "capillary effects" where, broadly speaking, interfacial energies induces flows and forces.
While the surface tension of these condensates is tiny compared to the surface tension of water droplets in air, the surrounding structures of proteins, filaments and membranes are also very soft and mobile. In fact, the cell finds itself at an fascinating length-scale, where small changes in the properties or size of the condensate or the environment can lead to changes in the system behavior: Small condensates may localize and stick to certain cellular structures whereas large condensates may bend filaments and membranes to induce shape changes in the cell.
(A nice review can be found here: https://doi.org/10.1038/s41586-022-05138-6 )
During my PhD with Eric Dufresne at ETH Zurich, I studied the interactions of stress granules, a cytosolic biomolecular condensate, with the filaments of the cytoskeleton. Using novel analysis methods and statistical physics approaches, we have been able to quantify wetting interactions between stress granules and tubulin, the molecular buildingblock of microtubules (the largest cytosolic filament). While the wetting interactions between stress granule and single tubulin proteins are weak and transient, a full microtubule shows significant wetting towards the stress granule leading to mutual deformations of the condensate and the microtubule network.
Filamentous (f-)actin, a thinner cytoskeletal filament with characteristic flow patterns, on the other hand, does not show such pronounced wetting behavior. Instead, f-actin is important for granule motion: Steric interactions between f-actin and stress granules move the condensates along the characteristic f-actin flow towards the center of the cell.
In 2023, I joined the lab of Roland Knorr at Humboldt-Universität zu Berlin, where we aim to understand and quantify capillary phenomena between biomolecular condensates, filaments and lipid membranes. We joined forces with groups from the Charité University Hospital and Oslo University Hospital to understand how capillary forces structure the cell and how such forces affect cell physiology.
Swimming Dynamics of C. reinhardtii (former)
Chlamydomonas reinhardtii are unicellular green algae with two anterior flagella. These flagella beat in a pattern similar to a human breaststroke. The flagella propel the cell in the direction of the flagella, making C. reinhardtii a "puller" type microswimmer, contrary to many bacteria which swim "cell body first" and are "pushers".
During my Bachelor thesis in the lab of Oliver Bäumchen, we studied the motion of C. reinhardtii in geometric confinement, where we identified curvature-guided motility patterns.
Throughout my Master thesis in the same lab, I developed micropipette force sensors for measurements of dynamic forces. Micropipette force sensors are hollow glass capillaries bent into a Z- or double-L-shape. Forces acting upon the tip of the pipette deflect it and, with the suitable calibration, allow to measure forces. During my thesis, I recorded the fluctuations of the pipette with a free-swimming algae at the tip. Using the fluctuation spectrum of the pipette deflection, we could quantify the energy associated to the periodically beating flagella. Placing the swimming algae at different distance to a solid interface, we have been able to quantify the magnitude of hydrodynamic interactions of the pair of beating flagella as a function of distance to the interface. Strikingly, we found that the flagella show increased force transduction at distanced larger than the extent of the flagella, highlighting the presence of hydrodynamic interactions.
Chlamydomonas reinhardtii are unicellular green algae with two anterior flagella. These flagella beat in a pattern similar to a human breaststroke. The flagella propel the cell in the direction of the flagella, making C. reinhardtii a "puller" type microswimmer, contrary to many bacteria which swim "cell body first" and are "pushers".
During my Bachelor thesis in the lab of Oliver Bäumchen, we studied the motion of C. reinhardtii in geometric confinement, where we identified curvature-guided motility patterns.
Throughout my Master thesis in the same lab, I developed micropipette force sensors for measurements of dynamic forces. Micropipette force sensors are hollow glass capillaries bent into a Z- or double-L-shape. Forces acting upon the tip of the pipette deflect it and, with the suitable calibration, allow to measure forces. During my thesis, I recorded the fluctuations of the pipette with a free-swimming algae at the tip. Using the fluctuation spectrum of the pipette deflection, we could quantify the energy associated to the periodically beating flagella. Placing the swimming algae at different distance to a solid interface, we have been able to quantify the magnitude of hydrodynamic interactions of the pair of beating flagella as a function of distance to the interface. Strikingly, we found that the flagella show increased force transduction at distanced larger than the extent of the flagella, highlighting the presence of hydrodynamic interactions.
