Functional organization of axonal actin
Thesis supervisor: Marie-Jeanne Papandréou (MCU AMU)
Co-director : Christophe Leterrier
State of the art
The overall goal of this project is to understand how actin shapes the organization and physiology of axons. In neurons, axons generate and propagate action potentials, transmitting signals to target cells. Their extraordinary architecture must be robust and adaptable, and this is ensured by a unique organization of the axonal cytoskeleton: microtubules, actin and neurofilaments (1). Axonal actin organization has recently been completely redefined by studies using optical super-resolution microscopy, notably Single Molecule Localization Microscopy (SMLM, a modality with ~20 nm resolution comprising techniques such as STORM, PALM, and DNA-PAINT). Actin forms regularly-spaced submembrane rings connected by spectrin tetramers, but the composition and assembly mechanisms of this periodic complex are still unknown. Moreover, we discovered that actin also forms dynamic intra-axonal clusters every 3-4 μm that we termed “hotspots” from which “trails” of filaments assemble and disassemble along the axon within seconds (2). Almost everything remains to be discovered about these axonal actin assemblies, most importantly their cellular functions (3).
The objective is to define the molecular organization of axonal actin structures and determine their functions for axonal growth, maintenance and transport.
The student will combine live-cell imaging, state-of-the-art multicolor SMLM and quantitative analysis approaches. This will allow to study identified actin structures from dynamics to nanoscale detail. Moreover, we will devise specific perturbation strategies that will be coupled to correlative imaging. We will determine molecular partners specific to each of the actin structures, selectively perturb them and determine the impact on axonal growth, maintenance and physiology.
This work will provide innovative correlative approaches (4) between live-cell imaging and super-resolution microscopy to decipher the neuronal architecture. The student will characterize the dynamics and interplay of identified axonal actin structures, as well as devise innovative analysis strategies (5) to obtain a quantitative, comprehensive model of axonal actin organization. The ultimate biological goal of this project is functional insight: identification of partners specific to each of the actin structure sand their selective perturbation will reveal the yet unknown functions of actin structures in the cellular physiology of the axon.
We are looking for a dedicated team player with a background in neuronal cell biology, advanced microscopy and/or image analysis.