Biomedicine Cell Structures in 3-D A new technique pushes the boundaries of super-resolution light microscopy. by Courtney Humphries February 9, 2009 Sponsored by With normal fluorescence microscopy, a single protein labeled with fluorescent molecules, such as this cell membrane protein, appears as a blurry spot. Using a technique called PALM, Harald Hess and colleagues can pinpoint the positions of many different membrane proteins in two dimensions. By adding another technique, called interferometry, to PALM, the researchers can also detect the vertical depth of each fluorescent protein in the image. The proteins have been color coded by vertical position: red is deepest and purple is the shallowest. The white boxes show cross sections of small pieces of the image, which reveal how membrane proteins separate into two layers at the top and bottom of the cell. The advantage of fluorescence microscopy is that it allows scientists to label and image specific proteins. Here, the iPALM technique is used to image integrins–proteins that allow the cell to adhere to surfaces. When a small slice of a cell with integrins labeled (top) is viewed in cross section (bottom), the three-dimensional organization of the molecules is revealed. Red and yellow areas are closest to the glass cover slip on which the sample has been placed; the yellow regions show areas where the integrins have attached to the glass. The networks of integrins seen in blue and purple are inside the cell where new proteins are being made.