Scanning X-Ray Nanodiffraction on Dictyostelium discoideum

by Marius Patrick Priebe
Doctoral thesis
Date of Examination:2015-02-04
Date of issue:2015-11-06
Advisor:Prof. Dr. Tim Salditt
Referee:Prof. Dr. Tim Salditt
Referee:Prof. Dr. Jörg Enderlein
Referee:Prof. Dr. Eberhard Bodenschatz
Referee:Prof. Dr. Sarah Köster
Referee:Prof. Dr. Simone Techert
Referee:Dr. Jochen S. Hub
Persistent Address: http://dx.doi.org/10.53846/goediss-5183

 

 

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Abstract

English

In the recent years, novel focussing optics for synchrotron radiation sources became available, which now allow focussing the x-radiation down to 100\,nm (FWHM). Thus, the typically poor spatial resolution of Small Angle X-ray Scattering (SAXS) has been overcome and enables "Scanning X-ray Nanodiffraction", where a sample is scanned in a linewise motion, while recording a far-field diffraction pattern at every scanning position. In this work, Scanning Nanodiffraction was applied to single cells of the amoeba \textit{Dictyostelium discoideum}, which is a model system for amoeboid migration, that is enabled by a reorganization of cytoskeletal biopolymers in the cell cortex. The spatially resolved small angle x-ray diffraction signal shows characteristic streak-like patterns in reciprocal space, which is attributed to fibre bundles of the actomyosin network. An anisotropy parameter nicknamed "Streak Finder" is introduced to characterize the pronounced local variations within the cell. The x-ray differential phase contrast is evaluated in terms of the projected electron density and additional x-ray fluorescence aquisitions provide information on the spatially resolved distribution (2D) of elements within the cell. The x-ray results are correlated with optical microscopy (phase contrast and fluorescence microscopy of strains with labelled actin and myosin II) on live, fixed, and cryogenic cells.
Keywords: Nanodiffraction; Dictyostelium discoideum; Actin; Myosin-II; Streak Finder; SAXS; STXM; Fluorescence mapping; Ptychography; X-ray; Vitrification; Frozen-hydrated cells; Sample preparation
 
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