Dynamics of novel feet of Dictyostelium cells during migration.

Kazuhiko S K Uchida,Shigehiko Yumura

doi:10.1242/jcs.01015

Abstract

We observed the dynamics of actin foci in live Dictyostelium cells expressing GFP-actin. Actin foci were dynamic structures, but they were fixed on the substratum during cell migration. Interference reflection microscopy revealed that the ventral cell membrane was closer to the substratum at sites of actin foci. Furthermore, some actin foci were incorporated into the retraction fibers, ripped off from the cells and eventually shed on the substratum after the cells moved away. The velocity of the cells was inversely proportional to the number of actin foci. Measurement of traction force using a silicone substratum demonstrated that the traction force was transmitted to the substratum through actin foci. Taken together, several lines of evidence strongly suggest that actin foci function as the active 'feet' of Dictyostelium cells. We also found evidence suggesting that changing step is regulated in a coordinated manner during cell migration. Possible mechanisms by which these cells migrate across substrata are discussed in this context.

Highlights

Cell migration plays a critical role in a variety of physiological processes including growth, development and wound healing
Focal contacts are composed of clusters of integrin, a transmembrane glycoprotein involved in cell-substratum adhesion, which are linked to the terminals of stress fibers through a series of linkage proteins, such as talin, vinculin, alpha-actinin and various signaling proteins (Burridge et al, 1988; Zamir and Geiger, 2001)
In our previous report, when Dictyostelium cells were allowed to migrate on a coverslip and stained with Concanavalin A (Con A), tracks with distinct patterns of dots and short fibers were observed behind the cells (Uchida and Yumura, 1999)

Summary

Introduction

Cell migration plays a critical role in a variety of physiological processes including growth, development and wound healing. Regulation of the attachment of cells to the substratum is essential for cell migration. The mechanisms underlying cellsubstratum adhesion have been investigated primarily in fibroblasts, which are slow-moving cells with an irregular shape. Interference reflection microscopy (IRM) has shown that many focal contacts are distributed on the ventral surface of fibroblasts (Curtis, 1964; Izzard and Lochner, 1976). Focal contacts are composed of clusters of integrin, a transmembrane glycoprotein involved in cell-substratum adhesion, which are linked to the terminals of stress fibers through a series of linkage proteins, such as talin, vinculin, alpha-actinin and various signaling proteins (Burridge et al, 1988; Zamir and Geiger, 2001). The actin filaments transmit traction force to the substratum at the sites of cell-substratum adhesion (Beningo et al, 2001; Burton et al, 1999; Munevar et al, 2001; Oliver et al, 1999; Perham and Wang, 1999)

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Conclusion