Abstract
Structural analysis of biological membranes is important for understanding cell and sub-cellular organelle function as well as their interaction with the surrounding environment. Imaging of whole cells in three dimension at high spatial resolution remains a significant challenge, particularly for thick cells. Cryo-transmission soft X-ray microscopy (cryo-TXM) has recently gained popularity to image, in 3D, intact thick cells (∼10μm) with details of sub-cellular architecture and organization in near-native state. This paper reports a new tool to segment and quantify structural changes of biological membranes in 3D from cryo-TXM images by tracking an initial 2D contour along the third axis of the microscope, through a multi-scale ridge detection followed by an active contours-based model, with a subsequent refinement along the other two axes. A quantitative metric that assesses the grayscale profiles perpendicular to the membrane surfaces is introduced and shown to be linearly related to the membrane thickness. Our methodology has been validated on synthetic phantoms using realistic microscope properties and structure dimensions, as well as on real cryo-TXM data. Results demonstrate the validity of our algorithms for cryo-TXM data analysis.
Highlights
Biological membranes provide specialized permeability barriers for cells and cell organelles, in which the interplay of lipids and membrane proteins facilitates basic processes of respiration, photosynthesis, protein and solute transport, signal transduction, and motility [1]
To evaluate the proposed membrane profile quantification from images produced by an X-ray microscope, we demonstrate, through synthesized phantoms (Section 3.2.1), how it scales with respect to the theoretical membrane thickness
The last set of experiments uses the measured data obtained from a synchrotron soft X-ray microscope, to investigate the feasibility of applying our method to real biological problems
Summary
Biological membranes provide specialized permeability barriers for cells and cell organelles, in which the interplay of lipids and membrane proteins facilitates basic processes of respiration, photosynthesis, protein and solute transport, signal transduction, and motility [1]. The cell membranes of almost all living organisms and many viruses are made of two layers of lipid molecules (a bilayer) containing various types of protein molecules, which are typically. Membrane quantification of intact thick cells using cryo soft X-ray transmission microscopy. Competitiveness, through the Maria de Maeztu Programme for Centres/Units of Excellence in R&D (MDM-2015-0502). We thank HZB for the allocation of synchrotron radiation beamtime. We thank Katja Henzler and Basel Tarek for their support during the data acquisition and pre-processing
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