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Modelling the structure and dynamics of cellular organelles with non-equilibrium dynamics
Membrane-bound organelles perform many essential functions in the cell, among which the sorting and biochemical maturation of cellular components. Organelles along the secretory and endocytic pathways are strongly out-of-equilibrium structures, which display large stochastic fluctuations of composition and shape resulting from inter-organelle exchange and enzymatic reactions. Understanding how the different molecular mechanisms controlling these processes are orchestrated to yield robust fluxes of matter and to direct particular components to particular locations within the cell is an outstanding problem of great interest for cell biologist, but also for physicists.
In this talk, I will discussed stochastic models of organelle self-organisation based on the simplified view that organelle dynamics results from a competition of two kinetic processes : vesicular exchange between organelles and maturation ; i.e. the change of biochemical identity of an organelle over time (early to late endosomes, cis to trans Golgi cisternae…). I will first describe in some details two specific processes relevant to organelle dynamics : the sorting of components by vesicular exchange, and the competition between maturation and exchange in a simple, one-compartment system. I will then discuss a conceptual model of organelle biogenesis and maintenance that include vesicular exchange (budding, transport, and fusion) and biochemical maturation. I will show how the non-equilibrium steady-state of an organelle or a network of organelles may be varied in a controlled manner by modifying a limited number of coarse-grained parameters (essentially, the budding, fusion and maturation rates) and discuss the relevance of these results for the structure of the Golgi apparatus.