2.6 Visualizing Sub-cellular Organization Using Soft X-ray Tomography

Abstract

Soft X-ray tomography is an imaging technique ideally suited to quantitatively visualizing subcellular organization, particularly in eukaryotic cells. With this technique, cells are visualized in three dimensions using X-rays in the ‘water window’ region of the spectrum. Image contrast is generated by the differential absorption of X-ray photons by the specimen. This results in quantitative high-contrast images of intact, fully hydrated cells without the use of contrast-enhancing agents. In soft X-ray tomography, the subcellular organization is therefore visualized in cells that are close to their native state. The development of correlated high numerical aperture cryogenic light microscopy allows the same specimen to be imaged using both visible light fluorescence and bright field transmission X-ray tomography. Using these two modalities in tandem allows tagged molecules to be localized in the context of a high-resolution three-dimensional tomographic reconstruction of the intact cell. This powerful combination of imaging techniques can be applied to a wide range of specimen types, from simple prokaryotes to large, complex eukaryotic cells, or even tissue sections.