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Reverse mathematical methods for reconstructing molecular dynamics in single cell

Drift, Wander, or Stick: Disentangling Modes of Organelle Motion in Living Cells

speaker: Elena Koslover (UCSD)

abstract: Eukaryotic cells utilize a variety of transport modes to distribute organelles within their cytoplasm. Individual organelles can be carried processively by molecular motors, exhibit random walk motion akin to diffusion, drift via advection in a flowing cytoplasmic fluid, or be tethered to stationary cellular structures. The efficiency and relative contributions of these different modes of transport can be estimated theoretically through a combination of stochastic simulations and physical modeling of the underlying fluid flows and forces that drive each mode. However generating such quantitative models requires the ability to categorize the motion of organelles observed in vivo and to accurately extract the parameters describing their motion. We will discuss how organelle trajectories extracted from fluorescent video microscopy data can be analyzed to gain quantitative insight into the sources of organelle motion.

In particular, we will demonstrate how to disentangle diffusive motion from slowly varying advective drift of lysosomal organelles in deforming motile neutrophils, using a wavelet-based methodology. A substantial contribution of deformation-driven cytoplasmic flow to the mixing of organelles in such cells is demonstrated using a simplified physical model parameterized from in vivo data. Additionally, we will show that diffusion, directed active transport, and tethering to intracellular structures all contribute to the dispersion of peroxisomes in fungal hyphae, and that much of the seemingly diffusive motion can be accounted for by hydrodynamic entrainment from passing motor-driven organelles. A method for distinguishing tethered from diffusive motion in short particle trajectories will be discussed. Our results highlight the importance of combining together diverse transport mechanisms for distributing organelles through eukaryotic cells, while establishing new approaches for identifying and quantifying the mechanisms at play in experimentally observed organelle trajectories.

Mon 15 Oct, 10:15 - 11:00, Aula Dini
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