Cell’s secrets coming to light –
The limitations to spatial resolution in light microscopy has been discovered – and named after – the German physicist Ernst Abbe in the 19th century. The so-called Abbe limit depends on the wavelength of light and makes it hard to achieve a resolution below 200 nanometer which equals 200 billionths of a meter. “Our trick was to use a structured illumination to cause what researchers usually try to avoid: an interference visible as a shadow pattern across the image,” says Leonhardt. “But since we knew the fine pattern of light we used for illumination, we could then calculate with some mathematics and a good computer the unknown details of the biological specimen.”
And they got some surprising details: The research team tested their novel approach with the nucleus of a mammalian cell. The result was a three dimensional image with doubly the resolution of conventional light microscopes. “It was – in my opinion – a fascinating and unprecedented view of a dividing cell shortly before the birth of two daughter cells”, recalls Leonhardt. “This is one of the most fundamental processes of life and therefore intensively studied by research groups, also because errors may cause cell death or, even worse, give rise to a tumor.”
The image shows a nucleus preparing for cell division. The genetic material is condensed into chromosomes which are clearly visible under the nuclear membranes – and with even some new details on their surface. Different layers of the nuclear envelope can be distinguished and two invaginations have appeared: “They are caused by structures called centrosomes which will shortly begin to pull the nuclear envelope apart,” explains Leonhardt. “The centrosomes will then pull the condensed chromosomes – one of a couple each – to their sides and thus distribute identical copies of the genetic material to the newborn daughter cells.”
The new technique even allows pictures and movies in 3D. In the future, it might be possible to capture whole processes on film as well. At the moment, 3D-SIM is the only imaging technique that can produce multicolour 3D images of whole cells with enhancement of resolution. “It is important for researchers to note that these results were obtained with standard methods to prepare and dye the cells and their structures,” stresses Leonhardt. “Also, the 3D-SIM microscope platform is not more difficult to use than conventional commercial microscopes.
The study was conducted on a prototype based on conventional microscope technology but commercial models should become available within a year. The possibility of using 3D-SIM with well-established standard labelling techniques and to simultaneously locate different molecules or structures in the three dimensional context and in multicolour will undoubtedly open interesting new perspectives for molecular cell biology and biomedical research alike.
“Subdiffraction Multicolor Imaging of the Nuclear Periphery with 3D Structured Illumination Microscopy”,
Lothar Schermelleh, Peter M. Carlton, Sebastian Haase, Lin Shao, Lukman Winoto, Peter Kner, Brian Burke, M. Cristina Cardoso, David A. Agard, Mats G. L. Gustafsson, Heinrich Leonhardt, John W. Sedat,
Science, online on June 6, 2008