Variation in cell-substratum adhesion in relation to cell cycle phases

The quantification of focal adhesion sites offers an assessable method of measuring cell–substrate adhesion. Such measurement can be hindered by intra-sample variation that may be cell cycle derived. A combination of autoradiography and immunolabelling techniques, for scanning electron microscopy (SEM), were utilised simultaneously to identify both S-phase cells and their focal adhesion sites. Electron-energy ‘sectioning’ of the sample, by varying the accelerating voltage of the electron beam, combined with backscattered electron (BSE) imaging, allowed for S-phase cell identification in one energy ‘plane’ image and quantitation of immunogold label in another. As a result, it was possible simultaneously to identify S-phase cells and their immunogold-labelled focal adhesions sites on the same cell. The focal adhesion densities were calculated both for identified S-phase cells and the remaining non-S-phase cells present. The results indicated that the cell cycle phase was a significant factor in determining the density of focal adhesions, with non-S-phase cells showing a larger adhesion density than S-phase cells. Focal adhesion morphology was also seen to correspond to cell cycle phase; with ‘dot’ adhesions being more prevalent on smaller non-S-phase and the mature ‘dash’ type on larger S-phase cells. This study demonstrated that when quantitation of focal adhesion sites is required, it is necessary to consider the influence of cell cycle phases on any data collected.