Academic literature on the topic 'Protein Dynamics - Confocal Microscopy'

Membrane protein dynamics is of great importance for living organisms. The precise localization of proteins composing a synapse on the membrane facing a nerve terminus is essential for proper functioning of the nervous system. In muscle fibers, the nicotinic acetylcholine is densely packed under the motor nerve termini. A receptor associated protein, rapsyn, acts as a linker between the receptor and the other components of the synaptic suramolecular assembly. Advances in fluorescence microscopy have allowed to measure the behavior of a single receptor in the cell membrane. In this work single-molecule microscopy was used to track the motion of ionotropic acetylcholine (nAChR) and serotonin (5HT3R) receptors in the plasma membrane of cells. We present methods for measuring single-molecule diffusion and their analysis. Single molecule tracking has shown a high dependence of acetylcholine receptors diffusion on its associated protein rapsyn. Comparing muscle cells that either express rapsyn or are devoid of it, we found that rapsyn plays an important role on receptor immobilization. A three-fold increase of receptor mobility was observed in muscle cells devoid of rapsyn. However, in these cells, a certain fraction of immobilized receptors was also found immobile. Furthermore, nAChR were strongly confined in membrane domains of few tens of nanometers. This showed that membrane composition and membrane associated proteins influence on receptor localization. During muscle cell differentiation, the fraction of immobile nAChR diminished along with the decreasing nAChR and stable rapsyn expression levels. The importance of rapsyn in nAChR immobilization has been further confirmed by measurements in HEK 293 cells, where co-expression of rapsyn increased immobilization of the receptor. nAChR is a ligand-gated ion-channel of the Cys-loop family. In mammals, members of this receptor family share general structural and functional features. They are homo- or hetero-pentamers and form a membrane-spanning ion channel. Subunits have three major regions, an extracellular ligand binding domain, a transmembrane channel and a large intracellular loop. 5HT3R was used as a model to study the effect of this loop on receptor mobility. Single-molecule tracking experiments on receptors with progressively larger deletions in the intracellular loop did not show a dependence of the size of the loop on the diffusion coefficient of mobile receptors. However, two regions were identified to play a role in receptor mobility by changing the fractions of immobile and directed receptors. Interestingly, a prokaryotic homologue of cys-loop receptors, ELIC, devoid of a large cytoplasmic loop was found to be immobile or to show directed diffusion similar as the wild-type 5HT3R. The scaffolding protein rapsyn stabilizes nAChR clusters in a concentration dependent manner. We have measured the density and self-interactions of rapsyn using FRET microscopy. Point-mutations of rapsyn, known to provoke myopathies, destabilized rapsyn self-interactions. Rapsyn-N88K, and R91L were found at high concentration in the cytoplasm suggesting that this modification disturbs membrane association of rapsyn. A25V was found to accumulate in the endoplasmic reticulum. Fluorescent tools to measure intracellular concentration of calcium ions are of great value to study the function of neurons. Rapsyn is highly abundant at the neuromuscular junction and thus is a genuine synaptic marker. A fusion protein of rapsyn with a genetically encoded ratiometric calcium sensor has been made to probe synapse activity. This thesis has shown that the combined use of biologically relevant system and modern fluorescence microscopy techniques deliver important information on pLGIC behaviour in the cell membrane.<br><p>QC 20151217</p>

This thesis work aspires to present a new concept for the application of correlation techniques to the study of the cellular environment. By exploiting local analysis in combination to a fast fit-free technique (the phasor approach) we provide an exhaustive high-resolution analysis of structural and dynamic properties while maintaining a reasonable computation time. The dissertation will be articulated as follows: In CHAPTER 1 we aim to provide the reader with a description of the techniques that will be exploited during the rest of the dissertation together with the open questions and problematics that our techniques will try to answer to. In CHAPTER 2 we present the local analysis concept and its application to a correlation technique capable of measuring size and concentration (ICS). We will show how we coupled ICS to the phasor approach to create a technique (PLICS) for the assessment of size heterogeneity. PLICS will be demonstrated with simulations as well as with cellular samples and will be applied to the study of endocytic vesicles uptake and to the characterization of other organelles. In CHAPTER 3 the concept is extended to two-colors samples for the determination of local inter-structure distance (PLICCS). We will present a pattern analysis method we developed that exploits this information in order to evaluate the relative distribution of the structures imaged in the two channels, comparing it to a random distribution. This method will be validated with simulations and applied to the study of replication-transcription collisions. Successively, we will show that PLICCS can be converted to a localization algorithm for single particle tracking that will be used for tracking membrane receptors in living neurons. CHAPTER 4 will describe the extension of our local analysis to RICS, a correlation technique capable of measuring the diffusion coefficient of a fluorescent probe. The resulting algorithm (L-RICS) provides high resolution diffusion maps that will be used to characterize the diffusion of a fluorescent probe (GFP) within the nucleus and nucleolus of living cells. We will show that the algorithm can be implemented also in non-linear scanning systems. CHAPTER 5 will conclude the dissertation by introducing advanced correlation methods for the analysis of non-Brownian diffusion and their coupling to super-resolution techniques. In particular, we will present a super-resolution correlation technique (SPLIT) recently developed capable of analyzing the cellular environment and a microcamera-based approach (Airyscan comprehensive correlation analysis) we developed for the parallel implementation, in super-resolution, of several complementary correlation techniques.