Invertiertes Lichtmikroskop mit TIRF-Modul
Final Report Abstract
We are interested in the Biological Physics of Cellular Systems and Soft Matter. In vivo studies of animal cells and slime molds are combined with in vitro investigations of model membrane systems. As a general framework, we use phases and phase transitions observed in these active biological systems. In particular, we want to understand active membrane waves in fibroblast cells, morphology and structure formation in slime molds, as well as thermal fluctuations of lipid membranes. We employ and develop advanced light microscopy. Image time sequences are analyzed using concepts from condensed matter physics and graph theory. The reflection interference contrast capability of the acquired instrument has been used to study cell membrane adhesion in early cell spreading. We found this phase of cell spreading to be characterized by transient adhesion patches with a typical mean size of 1 µm and a lifetime of 33 s. Eventually, these patches fuse to initiate extensive spreading of the cell. Digital time lapse movies are analysed employing spatio-temporal correlation functions of adhesion patterns. Correlation length and time can be scaled to obtain a master curve at the fusion point. Microplasmodia of slime molds show pronounced active fluctuations and fusion very well visible using phase contrast microscopy. These events eventually lead to percolation of an extended network. We studied the formation of transportation networks of the true slime mold Physarum polycephalum after fragmentation by shear. Small fragments, called microplasmodia, fuse to form macroplasmodia in a percolation transition. At this topological phase transition, one single giant component forms, connecting most of the previously isolated microplasmodia. Employing the configuration model of graph theory for small link degree, we have found analytically an exact solution for the phase transition. It is generally applicable to percolation as seen, e.g., in vascular networks. Further, we study cytoskeleton-membrane waves and ruffles using total internal reflection fluorescence (TIRF) and epifluorescence. The aim of the project is to quantitatively compare existing theories of active gels with experiments. We will study wave propagation as a function of the biochemical state of the cell.
Publications
- Adhesion patterns in early cell spreading. J. Phys.: Condens. Matter 22, 194106 (2010)
P. Ryzhkov, M. Prass, M. Gummich, J.-S. Kühn, C. Oettmeier, and H.-G. Döbereiner
- Physarum polycephalum percolation as a paradigm for topological phase transitions in transportation networks. Phys. Rev. Lett. 109, 078103 (2012)
A. Fessel, C. Oettmeier, E. Bernitt, N.C.L. Gauthier, and H.-G. Döbereiner
