Cytoskeletal control of fibroblast length: experiments with linear strips of substrate.

In order to understand the factors determining the length of fibroblasts, three cell lines (mouse embryonic fibroblasts plus human fibroblast lines AGO 1523 and M19) were cultivated on the usual planar substrate (glass) and on specially prepared narrow linear strips of the same substrate, where the cells could spread only linearly. Morphometric measurements showed that the average length of cells of each type on the 'unidimensional' strips was no different from that on the usual 'bidimensional' substrate. The addition of colcemid significantly decreased cell length on both substrates, whereas cytochalasin D increased the length. We concluded that fibroblasts have an intracellular mechanism maintaining a relatively constant average cell length. This mechanism may involve the dynamic balance of centripetal and centrifugal forces developed by two cytoskeletal systems: the microtubules and the actin-myosin cortex. Three epitheliocyte cell lines (rat IAR2, canine MDCK and bovine FBT) were tested but, in contrast to fibroblasts, they did not maintain similar cell lengths on the usual substrate and on the linear strips, suggesting that control of length is cell-type-specific.

Cylindrical substratum induces different patterns of actin microfilament bundles in nontransformed and in ras-transformed epitheliocytes.

The influence of the cylindrical substratum surface on the actin microfilament bundle and the extracellular matrix (fibronectin and laminin) patterns in nontransformed epithelial cells of the IAR-2 rat line and in their N-ras-transformed descendants, IAR-ras-c4 cells, was studied. The cells were cultured on substrata with cylindrical surfaces-fused quartz glass fibers with a diameter of 32 microm. Quantitative analysis of actin microfilament bundle alignment and immunomorphological study of fibronectin and laminin were used. IAR-2 epitheliocytes on the cylindrical substrata formed straight actin microfilament bundles and fibronectin- or laminin-positive fibrils aligned predominantly transversely to the cylinder axis. In contrast, in the majority of IAR-ras-c4 cells on the cylindrical substrata, the revealed straight microfilament bundles and the fibrils of the extracellular matrix were oriented approximately longitudinally to the cylinder axis; a small part of the transformed cells formed microfilament bundles and extracellular matrix patterns similar to those in the normal epitheliocytes on the cylindrical substrata. These results show that transformed epitheliocytes that acquired polarized morphology react to the curvature of the cylindrical substratum surface by actin cytoskeleton and extracellular matrix reorganization changes essentially different from those characteristic of normal discoid epitheliocytes on the cylindrical substrata, but similar to those observed in normal polarized cells, e.g., fibroblasts.