Cells adhere to the extracellular matrix through focal adhesions (FAs). These act as anchors for the intracellular stress fibres that generate the force necessary for cell migration and also function as signalling centres through which extracellular signals are transduced by integrin molecules. On , Clemens Franz and Daniel Müller use fluorescence microscopy and atomic force microscopy (AFM) to reveal the ultrastructure of FAs for the first time. To gain access to the FAs, the authors `de-roofed' fibroblast cells expressing YFP-linked paxillin, a cytoskeletal protein present in FAs, by using gentle sonication to remove the upper surface of the cell and its intracellular organelles. They then used fluorescence microscopy to identify FAs before examining them by AFM, which allows high-resolution analysis of cellular structures under near-physiological conditions. Their work provides detailed insights into the 3D arrangement of microfilaments in FAs, the height and volume of FAs, and the localization of paxillin in the membrane-proximal part of the FA.
