A Micro-scope on intracellular trafficking

The general aim of this thesis work is to gain an encompassing insight into the intracellular trafficking machinery of multicellular organisms. For this purpose, the previously well-described model organism Caenorhabdits elegans is analyzed in our studies, with a focus on the family of small Rab-GTPases. These Rab-proteins (RABs) are the central players that orchestrate all intracellular trafficking events. An introduction to the current understandings in this field of science is given in the introductory chapter I. This thesis work began with a morphological description and a behavioral characterization of mutants of all members of rab-gene (rab) family. The major technique used for this anatomic investigation on the cellular- and subcellular level was two- as well as three-dimensional electron microscopy of high-pressure frozen nematode with a near-native sample-preservation. An atlas comprising all morphological data together with the results of additional behavioral studies, is the ultimate outcome of this thesis work. Among the descriptions of several tissues and organelles, the findings that the Golgi shapes seems to adapt to the activity in a tissue-specific manner is of central importance as it suggests that intracellular transport processes must also be investigated in a tissue-specific fashion. The generated tissue- and Rab-Atlas, along with all related results, is presented in chapter III, while a detailed description of used materials and methods is given in chapter II. During the entire investigation a special focus was directed towards the ultra-fast trafficking events that ensure the transmission at synapses. To aid these studies, the image analysis tool XtraCOunt was generated during this thesis work in order to semi-automates the analysis of these trafficking studies. Chapter IV describes this tool along with all its features. In the atlas studies the rab-10 mutant was identified as potentially neuronally impaired. In chapter IV, this mutant is examined for its synaptic features and it has been found to resemble the rab-2 mutant alterations in dense-core vesicle biogenesis. XtraCOunt was conceived for the analysis of electron micrographs of nematode synapses but was shown to be applicable in a vast range of other trafficking studies. Current collaborating studies, using this tool, led to the understanding of the phenotype of Sydney Brenner's first described mutant dpy-1 (dumpy), whose cuticular components are not able to maintain their network integrity. The fundamental findings of this study are presented in chapter V. To overcome imaging-constrains presented by the mostly electron microscopic nature of my study, I have furthermore tested the possibility of studying high-pressure frozen specimen with x-rays. High resolution phase contrast imaging, holo-tomography as well as micro-fluorescence investigations were tested for their applicability, feasibility and limitations. Their underlying mathematical theory and the obtained experimental results are presented and discussed in chapter VI. The major results of these investigations is a full-worm-tomogram with subcellular resolution and a map of tissue-specific elemental distributions within worm thin-slices. The concluding chapter VII briefly summarizes the results of all performed investigations in the context with one another and their possible meaning for the intracellular trafficking community.