Cell imaging, through the use of a plethora of imaging techniques and an ever-improving and -expanding range of fluorescent-molecule technologies, has become an essential and fast-moving area of modern cell biology. In the Journal of Cell Science, Paul Wiseman, Claire Brown and colleagues describe their contribution to this exciting field through their development and extension of the technique of image correlation microscopy (ICM), which they used to analyse integrin dynamics and interactions during cell migration.

ICM is derived from fluorescence correlation microscopy (FCS), and is used to measure spatial fluctuations in fluorescence intensity from images that have been obtained by laser scanning confocal microscopy. Correlation analysis is then used to calculate the various properties and interactions of a fluorescently tagged molecule. In the past, ICM was used mainly on fixed cells, but this research team have improved the technique by using 'retrospective image correlation', in which a time series of images taken from living (and, in this case, migrating) cells is analysed retrospectively. This allows the production of spatial maps of the concentration, aggregation state, interactions and transport properties of fluorescently tagged molecules within a cell. By using ICM to calibrate fluorescence intensities, the authors were also able to estimate the molecular densities (which includes information on molecular clustering) of integrins in adhesions. And, directional correlation analyses were used to study the net direction and speed of non-random molecular movements.

In this study the authors used ICM to analyse the behaviour of α5-integrin in migrating cells. They showed that integrins are present in sub-microscopic clusters of 3–4 molecules throughout the cell before they become discernably organized. In nascent focal adhesions, integrins become much more clustered and concentrated as well as less mobile, and, in fact, they seem to nucleate focal adhesions. Image cross-correlation microscopy (ICCM), in which the cross correlation between two images with different fluorescent signals is computed, was also used to show that α5-integrin and α-actinin reside in a complex even when they are not visibly organized. Furthermore, ICM was able to reveal interesting differences in the transport properties of the focal-adhesion components integrin, α-actinin and paxillin during focal-adhesion disassembly.

ICM and ICCM are extremely powerful techniques that can be used to provide spatial and temporal maps of several physical properties of, and interactions between, cellular components. And, as the images can be analysed both retrospectively and quantitatively, it has important implications for techniques such as high-throughput cellular screens and cellular modelling. This new cellular-imaging technology therefore promises huge potential for the analysis of complex biological phenomena.