Simulation and estimation of intra-cellular dynamics and trafficking

Le CD-ROM contient des données iconographiquesInternational audienceIn this chapter, we present an original modeling framework for membrane trafficking modeling and video-microscopy. Understanding the complexity of cellular processes requires a better knowledge of their dynamic properties and geometric structures. Over the last decade, progresses in cellular and molecular biology as well as in microscopy allow cell visualization while acquiring multidimensional data of their fastly occurring activities. The proposed method is devoted to the analysis of the dynamical content of microscopy image sequences corresponding to dynamical events related to membrane transport. This chapter is organized as follows. In Section 7.1, the major biological issues are introduced, as well as the optical instruments used for investigation. In this chapter, video-microscopy reveals the dynamical behavior of tagged proteins within the living cell. To capture the movements of these proteins, we propose new models to mimic trafficking of proteins within the cell by making the analogy with computer networks or road networks (Section 7.2). In addition, we provide a framework for simulating the foreground and background components observed in real image sequences. Section 7.3 is dedicated to the estimation of the background model. In Section 7.4, we consider the problem of estimating the origin-destination probabilities of the tagged proteins for the trafficking networ

Ecology and behaviour of the larvae of the Queensland fruit fly, Dacus tryoni. (Frogg.).

Organization of signalling molecules in biological membranes is crucial for cellular communication. Many receptors, ion channels and cell adhesion molecules are associated with proteins important for their trafficking, surface localization or function. These complexes are embedded in a lipid environment of varying composition. Binding affinities and stoichiometry of such complexes were so far experimentally accessible only in isolated systems or monolayers of cell culture. Visualization of molecular dynamics within signalling complexes and their correlation to specialized membrane compartments demand high temporal and spatial resolution and has been difficult to demonstrate in complex tissue like brain slices. Here we demonstrate the feasibility of single-particle tracking (SPT) in organotypic brain slices to measure molecular dynamics of lipids and transmembrane proteins in correlation to synaptic membrane compartments. This method will provide important information about the dynamics and organization of surface molecules in the complex environment of neuronal networks within brain slices

Deconvolving Active Contours for Fluorescence Microscopy Images

We extend active contours to constrained iterative deconvolution by replacing the external energy function with a model-based likelihood. This enables sub-pixel estimation of the outlines of diffractionlimited objects, such as intracellular structures, from fluorescence micrographs. We present an efficient algorithm for solving the resulting optimization problem and robustly estimate object outlines. We benchmark the algorithm on artificial images and assess its practical utility on fluorescence micrographs of the Golgi and endosomes in live cells

NMDAR-dependent long-term depression is associated with increased short term plasticity through autophagy mediated loss of PSD-95.

Long-term depression (LTD) of synaptic strength can take multiple forms and contribute to circuit remodeling, memory encoding or erasure. The generic term LTD encompasses various induction pathways, including activation of NMDA, mGlu or P2X receptors. However, the associated specific molecular mechanisms and effects on synaptic physiology are still unclear. We here compare how NMDAR- or P2XR-dependent LTD affect synaptic nanoscale organization and function in rodents. While both LTDs are associated with a loss and reorganization of synaptic AMPARs, only NMDAR-dependent LTD induction triggers a profound reorganization of PSD-95. This modification, which requires the autophagy machinery to remove the T19-phosphorylated form of PSD-95 from synapses, leads to an increase in AMPAR surface mobility. We demonstrate that these post-synaptic changes that occur specifically during NMDAR-dependent LTD result in an increased short-term plasticity improving neuronal responsiveness of depressed synapses. Our results establish that P2XR- and NMDAR-mediated LTD are associated to functionally distinct forms of LTD