Transmission X-ray microscopy of intact hydrated PtK2 cells during the cell cycle.

Transmission X-ray microscopy makes it possible to investigate biological specimens, i.e. cells and organelles, in their natural wet environment. The main processes determining the contrast in X-ray microscopy are photoelectric absorption and phase shift. X-ray microscopic experiments can therefore be carried out in both amplitude and phase contrast. The Göttingen X-ray microscope at the BESSY storage ring in Berlin is described. PtK2 cells were examined during different stages of the cell cycle. All major constituents of the mitotic apparatus, e.g. chromosomes, centromeres, microtubules and centrosomes, could be visualized, as well as the main structural compartments and organelles of the interphase cell, e.g. nuclear membrane, interphase chromatin, nucleolus and cytoplasmic mitochondria, as well as parts of the cytoskeletal apparatus. In this way new information can be obtained with regard to the ultrastructure of the constituents of intact and unstained cells at a resolution which bridges the gap between light microscopy and electron microscopy. The prospects for the future application of transmission X-ray microscopy in biomedical research are discussed.