NETWORK TOMOGRAPHY AND MINIMAL PATHS FOR TRAFFIC FLOWESTIMATION IN MOLECULAR IMAGING

International audienceGreen Fluorescent Protein (GFP)-tagging and time-lapse fluorescence microscopy enable to observe molecular dynamics and interactions in live cells. Original image analysis methods are then required to process challenging 2D or 3D image sequences. To address the tracking problem of several hundreds of objects, we propose an original framework that provides general information about molecule transport, that is about traffic flows between origin and destination regions detected in the image sequence. Traffic estimation can be accomplished by adapting the recent advances in Network Tomography commonly used in network communications. In this paper, we address image partition given vesicle stocking areas and multipaths routing for vesicle transport. This approach has been developed for real image sequences and Rab proteins

Patch-Based Markov Models for Event Detection in Fluorescence Bioimaging

International audienceThe study of protein dynamics is essential for understanding the multi-molecular complexes at subcellular levels. Fluorescent Protein (XFP)-tagging and time-lapse fluorescence microscopy enable to observe molecular dynamics and interactions in live cells, unraveling the live states of the matter. Original image analysis methods are then required to process challenging 2D or 3D image sequences. Recently, tracking methods that estimate the whole trajectories of moving objects have been successfully developed. In this paper, we address rather the detection of meaningful events in spatio-temporal fluorescence image sequences, such as apparent stable "stocking areas" involved in membrane transport. We propose an original patch-based Markov modeling to detect spatial irregularities in fluorescence images with low false alarm rates. This approach has been developed for real image sequences of cells expressing XFP-tagged Rab proteins, known to regulate membrane trafficking

Doctor of Philosophy

dissertationThe nervous system is comprised of an estimated 100 billion individual neurons, which are connected to one another to form a network that senses environmental stimuli and coordinates the organism's behavior. Because of the complexity of the nervous system, deciphering the developmental processes and adult wiring diagram has proved challenging. A number of axon guidance molecules have been identified; however, the means by which they guide billions of axons to their target cells in vivo remains poorly understood. Several axon guidance molecules have been found to be bifunctional, meaning they can elicit different growth cone responses depending on the presence or absence of other molecules, such as growth cone receptors, intracellular signal transduction molecules, or extracellular modulators. Axon sorting within axon tracts is perhaps a means by which axons are presorted to make a precise connection on their target cells. The zebrafish, Danio rerio, is an ideal model organism to study vertebrate axon guidance and axon sorting due to its external fertilization, optical transparency, amenability to forward genetics, and ease of making transgenic lines. In order to study axon guidance within the zebrafish retinotectal system, I developed a new method of misexpressing genes. Local misexpression can be induced by using a modified soldering iron in transgenic zebrafish in which a gene of interest is driven by a heat shock promoter. This method allowed me to examine the mechanisms by which Slit1a and Slit2 guide axons from the retina to the optic tectum. I determined the expression pattern of Slits in the zebrafish and used antisense morpholino technology to knock down Slit1a. The iv resultant axon guidance errors indicated that Slit1a acts to guide retinal axons through the optic tract. I then misexpressed Slit1a and Slit2 near the optic tract to observe their effect on axons. I found that both proteins appeared to attract retinal axons. Additionally, I saw that Slit2 seems to attract retinal axons earlier in the retinotectal pathway, at the optic chiasm. I also report on a new method, to whose development I contributed, for automated tracking of axons through electron microscopy datasets. Taken together, my results add new methods to the endeavor of mapping neural connectivity and development, and suggest a new role for Slits in axon guidance