Cryo-electron tomography

The cryo-electron tomography ( from Greek κρυος frost, ice, τομή "cut" and γράφειν " write") is an imaging technique for three-dimensional representation of the finest structures. It is used in particular in the study of cell structures in biology and medicine.

The cell assembly can be viewed without a change in the structure directly by chemical pretreatment, staining or thin sections.

A complete system for cryo-electron tomography costs about three million euros.

Operation

First, the object is cooled by using liquid nitrogen or helium, to up to four degrees Kelvin. The lightning-like freezing is thus given spatial structure of all cell components. At the same time prevents the cells burst in the subsequent investigation in the vacuum of an electron microscope. A vacuum is required since electron beams are deflected by gas molecules or dust.

After fixation of the specimen in the electron microscope are recorded with a high-resolution CCD sensor, two-dimensional images of the object from many different viewing directions and planes. Electrons have a much shorter wavelength than visible light, so structures can be resolved with an extension of up to four nanometers.

For the subsequent presentation of the cell structures in space as many frames are needed. However, in order to simultaneously increase the irradiation time. A computerized control this parameter prevents charring of the sample prior to the conclusion of the investigations.

Using special software, the series recordings obtained are later converted into a three-dimensional image.

History

The cryo-electron tomography was from 1987, developed by a research group led by one of the directors of the Max Planck Institute for Biochemistry in Martinsried near Munich, Wolfgang Baumeister. It was initially unclear whether cell components are three-dimensionally displayed in a size of a few nanometers. In intensive preparatory work with proteins whose structure was known, both recording technique and image analysis were optimized and automated.

From 2002, new insights into the communication and interaction of various molecular complexes and organelles inside a cell could be obtained with this technique. Wolfgang Baumeister was awarded for the development of cryo-electron tomography in 2006 with the Ernst Schering Prize. 2007 succeeded with the help of cryo-electron tomography for the first time the investigation of a complete single-celled organism with a nucleus and cell membrane.

Application

Cryo-electron tomography with the intact cell structure may be examined on a molecular level. It provides the higher resolution much deeper insights into the cell structure than the conventional light microscopy. The aim of the research architect is " the complex model of the entire cell to describe not only the functions of individual molecules and organelles, as has hitherto been possible, but the total cell structures ".

Currently, the process leads to a number of new discoveries in cellular, neural and infection biology, such as the representation of unknown structures in the cytoskeleton of malaria parasites.