Cytoplasmic Actins β and γ are Differentially Distributed in Stationary and Motile Cells

We have compared the distribution of β‐ and γ‐cytoplasmic actins in highly motile cells using laser confocal microscopy and newly developed β‐ and γ‐cytoplasmic actins monoclonal antibodies as well as the commercially available β‐actin antibody (clone Ac74). When fibroblastic, epithelial or endothelial cells attach on a substrate, divide, move into a wound, they have to organize their actin cytoskeleton in different types of structures such as in cell protrusions, in stress fibers or in circular bundles, e.g., during spreading. Interestingly, β‐ and γ‐cytoplasmic actins get organized in a complete different way, spatially and structurally. γ‐Cytoplasmic actin is mainly organized as a network under the dorsal membrane and in motile part of the cell (e.g., in lamellipodia); on the other hand, β‐actin is detected in the basal but not in the dorsal portion of the cell, is organized in radial cables at the cell‐cells contact in epithelial cells, in stress fibers in fibroblastic and endothelial cells and in circular bundles during cell spreading. It is known that the only sequence differences between the two cytoplasmic actins concern four amino acids located at the N‐terminus nonapeptide. Our results suggest that the N‐terminal domain of cytoplasmic actins are of major importance in allowing their differential cellular organisation in distinct cell activities, probably through an interaction with specific actin binding proteins.