Quantitative analysis of cell cycle progression

Analysis in time lapse microscopy of centrosomes with centrin1-GFP expressing HeLa cells shows that spindle orientation in the early stages of mitosis shows high variability:  Centrosomes don't seem to adopt a precise orientation with respect to any spatial cues as long as the nuclear envelope is still present. Final orientation of the mitotic spindle occurs during the later steps of mitosis, right after nuclear envelope breakdown and once the cell is completely rounded. This brings the conclusion that the mitotic cell conserves the information of its pre-established interphase adhesion pattern.

The retraction fibers play a role in this “memory”. Cortactin and ezrin previously located at the adhesive apices of the patterns accumulate respectively along the retraction fibres and at the proximal base of the RF on the cortex of the mitotic cell. Thus, RFs support the transfer of the adhesive pattern onto the mitotic cell body.

The figure below shows the significant drop in variability when analyzing the same event in cells on a homogeneous substrate and cell on micropatterns.