Mesoscopic Physics of Living System
Previous and Current Research
Cells have to control and switch biological function. In some cases this is achieved by the formation of chemically distinct compartments. Recent evidence suggests that there is a class of compartments, which can be regarded as liquid-like droplets formed by phase separation from the cellular cytoplasm. Within a large group of researchers in the Dresden area including Prof. Frank Jülicher (Max-Planck Institute for the Physics of Complex Systems) and Prof. Anthony Hyman (Max Planck Institute of Molecular Cell Biology & Genetics) we investigate the question of how cells use liquid phase separation and phase transitions to form chemically distinct non-membrane bound compartments inside cells and how cells control the position of these compartments in space using concentration gradients of regulating proteins [Annual Reviews, 30: 39–58].
In the specific case of the C. elegans embryo we could understand the mechanistic principles of how the MEX-5 protein concentration gradient spatially controls phase separation of P granule compartments [Cell, 6, 166: 1572–1584]. From a theoretical perspective, the concentration gradient leads to a spatially inhomogeneous scenario of droplet ripening, which can be described by an extension of the classical ripening theory of Lifschitz & Slyozov [New J. Phys., 19, 053021]. In addition, we found that the switch of position can be understood as a first order phase transition [arXiv:1704.07276].
Further interests are devoted to the influence of chemical reactions and external control parameters such as temperature and pH on the stability and dynamics of these liquid-like compartments. The presence of chemical reactions can affect the stability of liquid-like drops and even drive the division of droplets [Nature Physics, 13(4), pp.408-413.]. This finding indicates that liquid droplets combined with chemical reactions might have played a fundamental role in the evolution of protocells. The stability of liquid-like compartments is also influenced by changes in pH, which affects the interactions between components and can thereby drive phase separation in when pH is close to the isoelectric point (manuscript in preparation). Non-membrane bound compartments are not necessarily liquid droplets. They can undergo a solidification transition leading to phenomena reminiscent of (de) swelling of gels. A novel physical instability has been identified recently [arXiv:1710.03633].
Future Projects and Goals
A strong focus of my group is devoted to the physics of intra-cellular organization. In particular, the aim of my group is to identify and understand the mechanisms underlying the assembly, positioning and ageing of organelles. To this end, we use concepts from the fields of phase transitions, hydrodynamics and elasticity theory, but also develop new approaches to describe these systems. A central challenge is to identify the minimal ingredients to understand the physics underlying intra-cellular organization. This includes one fundamental question when physics meets biology: Does the considered living system behave similar to a thermal equilibrium systems or are there clear signatures that the system is driven and favors non-equilibrium states. In other words, how much is the intra-cellular organization different to the demixing of a vinaigrette, the hardening of a drying gelatin block or the sedimentation of droplets in the gravitational field?
Methodological and Technical Expertise
- Phase transitions and phase separation
- Hydrodynamic theories
- Theory of active matter
- Kinetic theory
- Pattern formation and non-linear dynamics
Christoph A. Weber, Chiu Fan Lee and Frank Jülicher
Droplet Ripening in Concentration Gradients
New J. Phys. 19, 053021 (2017)
David Zwicker, Rabea Seyboldt, Christoph A. Weber, Anthony A. Hyman and Frank Jülicher
Growth and Division of Active Droplets Provides a Model for Protocells
Nature Physics, 13(4), pp. 408–413
Shambaditya Saha, Christoph A. Weber, Marco Nousch, Omar Adame-Arana, Carsten Hoege, Marco Y. Hein, Erin Osborne-Nishimura, Julia Mahamid, Marcus Jahnel, Louise Jawerth, Andrej Pozniakovski, Christian R. Eckmann, Frank Jülicher, and Anthony A. Hyman
Polar Positioning of Phase-Separated Liquid Compartments in Cells Regulated by an mRNA Competition Mechanism
Cell 166, 6, 1572–1584 (2016)
Christoph A. Weber, Yen Ting Lin, Nicolas Biais and Vasily Zaburdaev
Formation and Dissolution of Bacterial Colonies
Phys. Rev. E, 032704 (2015)
Anthony A. Hyman, Christoph A. Weber, Frank Jülicher
Liquid-liquid phase separation in biology
Annu. Rev. Cell Dev. Biol., 30:39–58 (2014)