Length control is determined by the pattern of cytoskeleton

Abstract

In our previous experiments with linear strips of adhesive substrate, we found that elongated cultured fibroblasts preserve their length regardless of cell width and the number of cytoplasmic processes. This constancy of length was called 'length control'. In contrast to fibroblasts, single cultured epitheliocytes have nearly discoid shape on the plane substrata and have no length-controlling mechanism: their length on the narrow strips of adhesive substrate increased significantly in comparison with the diameter on the plane substrate. These results suggested that control of length is cell specific. An alternative suggestion is that length control is associated not with the cell type but with the cell cytoskeletal pattern (namely, with epithelioid circular actin bundles or straight actin bundles). Experiments described in this paper were made to choose between these two suggestions. Mouse embryo fibroblasts spreading on the planar substrate first acquire discoid epithelioid shape with a circular actin bundle. Only later did they acquire a polarized shape with straight actin bundles. Polarized, fully spread fibroblasts temporarily acquire discoid epithelioid shape when treated with the Taxol, disorganizing microtubules. However, epithelial discoid cells can be transformed into elongated fibroblast-like cells by scatter factor (HGF/SF; a cytokine) and by agents inhibiting Rho kinase. These reversible transitions from fibroblastic to epithelioid shape and vice versa were accompanied by a corresponding disappearance and appearance of length control. Fibroblasts with stress fibers destroyed by the Rho-kinase inhibitor Y27632 became considerable longer on the adhesive strips than on the plane while retaining a near-polarized shape. Thus, length control is typical not of the cell origin but of the cell phenotype (i.e. for polarized cells with microtubules and intact actin cytoskeleton.