On the Role of Microfilaments In Cell‐Shape‐Mediated Growth Control of Lens Epithelial Cells

With regard to the fact that, in anchorage‐dependent lens epithelial cells, DNA synthesis can be switched on and off by cell flattening and cell rounding, respectively, the state of the microfilaments has been followed by labelling actin with FL‐phalloidin during cell‐shape alterations. Cell flattening proved to be accompanied by both a structural organization of actin filaments into stress fibres and an enlargement of the area of the cell nucleus. Cell rounding, on the other hand, caused the microfilament bundles to disappear and the area of the nucleus to become smaller. From the time course of the inhibition of DNA synthesis by cytochalasin B, it was inferred that functionally intact microfilaments are required for the entrance of the cells into DNA synthesis but not for the maintenance of ongoing DNA synthesis. the assumption has been made that the tension, generated by microfilaments during cell spreading, will affect the state of the plasma membrane as well as the shape and the structure of the nucleus, which in turn seems to be preparatory for cells to enter the cycle.