Thickness and dynamic of the cell cortex

Thickness and dynamic of the cell cortex

By In Aiv Internship On July 27, 2018

Internship title: Thickness and dynamic of the cell cortex

Name: Physique et Mécanique des Milieux Hétérogènes (PMMH)
Affiliation: ESPCI-CNRS
Address: Sorbonne Université, Barre Cassan A, 7 quai St Bernard 75005 Paris France

LAB Director
Phone number: 0140794522

Phone number: 0140794719

Subject Keywords: biophysics
mechanical properties
magnetic particles
Tools and methodologies: Cell biology, microscopy, force measurement, magnetic forces
Summary of lab’s interests: With this project we aim to understand the cell cortex, an actin network underlying the cell plasma membrane. It is mostly composed of actin, various crosslinker, and myosin motors. This actin network give the cell its mechanical rigidity, but the rapid turnover of the proteins involved and the contractile myosin motors also allows for rapid deformation thus making the cortex an essential actor in cell morphology. Knowing the thickness and mechanical properties of this cortex is then important to understand the mechanics and deformability of the cell. Moreover the cortex is an active structure with different actin polymerization phenomena, such as actin waves, ruffles or confinement induced actin network. These dynamical structures are necessary for the cells to accomplish its functions, especially for probing and migrating in a complex environment.
Project summary: Because of the difficulty to probe it independently of the rest of the cell, the cortex and its mechanics are not well known. We developed a new tool to study the behavior of the cortex to understand these different types of activities and the mechanics behind complexes actin structures. We use super-paramagnetic beads that self-organize under a controlled magnetic field: in this situation, the beads are attracted to each other with a known force. Thanks to the ability of some cell types to engulf such objects we can create a system where we have one bead inside the cell and one outside. By this method we can confine the membrane and the cortex between these beads and track their position with tens of nanometer precision, thereby measuring directly the thickness of the cortex in time.
Until now we mostly concentrated on the observation and comprehension of the highly dynamic cortex of the dendritic cells, and started testing its mechanical properties. The aim of this internship will be to study other cell types (such as Dictyostellium or Drosophilia S2 cells) in order to question the universality of the observed phenomenon: is the cortex behaving the same way in other cells? A great advantage of these two cell types is the genetic toolbox available for the production of mutants, especially ones with different cortex composition and dynamics to try to decorrelate mechanical properties of the cortex from it’s activity.
Interdisciplinary aspect of the project: This interdisciplinary project aims at understanding the biophysics of cell cortex by combining tools from physics and biology. It is a collaboration between the PMMH lab (Physics and mechanics of heterogeneous media) in ESPCI/UPMC and the Systems Biology of Cell Polarity and Cell Division in Institut Curie.