Title: Cell polarisation, anomalous diffusion and chemotaxis in eukaryotic cells

Speaker: Prof. Manoj Gopalakrishnan, Department of Physics, IIT Madras

Abstract: Chemotaxis is a common mode of motility found in both prokaryotic and eukaryotic cells, by which a cell tries to follow a chemical gradient upstream or downstream. The underlying mechanism of chemotaxis in eukaryotes such as the amoeba Dictyostelium is fundamentally different from the well-studied run and tumble walk in bacteria. Eukaryotic cells ``polarise" when exposed to an external gradient by non-uniform localisation of intracellular signaling molecules. Generation of this internal polarity vector, or ``chemical compass", guides the motion of the cell by its coupling to actin polymerisation. Interestingly, in the absence of a gradient of chemo-attractant, many eukaryotic cells have been found to move about randomly in a super-diffusive manner, characterised by long-range correlations in velocity. Using a simple, perfect absorber model of a cell, we argue that random motion of such cells is generically super-diffusive in character, which can be traced to fluctuations in the cell's spontaneous polarity originating from Poissonian fluctuations in the local density of chemo-attractant molecules in the environment. The model also predicts a long-range, repulsive, effective interaction between different cells, which could be important in the interpretation of experimental data on collective motion.