Changing patterns of actin localization during cell division.

Abstract

Changing patterns of actin localization have been studied on a light microscopic level by means of fluorescently labeled heavy meromyosin. The cellular distribution of actin is characterized by four major patterns, each of which corresponds to a particular phase of cell division. Long actin fibers are a prominent feature of the interphase cell. They disappear as the cell rounds up for mitosis and are replaced by a diffuse distribution of actin throughout the cytoplasm. During cytokinesis, the actin is localized predominantly in the cleavage furrow. The final shift of actin occurs after the completion of cytokinesis. At this time the actin becomes concentrated in the distal poles of the cell where pseudopods form to pull the daughter cells apart. When the daughter cells have separated, they flatten on the culture dish and the fibrous pattern of actin characteristic of interphase cells returns. All of these changes take place during the 1-hr period required for cell division.

Comparison of purified anti-actin and fluorescent-heavy meromyosin staining patterns in dividing cells.

“…Previous reports of bright fluorescent-HMM staining of the cleavage furrow of similar cultured cells (20) may be the result of selective actin extraction from the adjacent cytoplasm during glycerination. There is no question that a circumferential band of actin filaments, the contractile ring, is concentrated in the cleavage furrow (22,20). It seems possible that cortical actin, adjacent to the contractile ring, has gone unnoticed by electron microscopy because it is poorly preserved or less well organized than the contractile ring actin filaments.…”

“…The evidence for actin in the mitotic spindle is more controversial. Although fluorescent HMM (19,20,9) and anti-actin sera (1) stain the spindle, relatively few 6-nm filaments are found in spindles prepared for electron microscope observation (4, 22, 10, 23, 2l).…”

“…Using an indirect fluorescent antibody staining technique, workers have found that immunoglobulins from these immune sera bind to a number of cellular structures including stress fibers (14,12,13,1,15), ruffled membranes (13,18), and the mitotic spindle (1). In the case of stress fibers there is little doubt that actin is present, because these fibers consist of bundles of 6-nm filaments that bind heavy meromyosin (HMM) (19,20,9) and subfragment-1 (S-I) (7,21). The evidence for actin in the mitotic spindle is more controversial.…”

A permeabilized cell model for studying cytokinesis using mammalian tissue culture cells

“…Unfortunately, these experiments were not performed in a manner that allows one to estimate the calcium requirements for cleavage . Although glycerol has been used extensively since Hoffman-Berling's time for the preparation of cytoskeletons for HMM decoration (11,30,32) and to study fibroblast movement in culture (11), the glycerinated cell preparations have not been used successfully to study cleavage in vitro. Given the importance of cleavage in cell division and our lack of knowledge about how this and other motile processes are regulated in nonmuscle cells, it would be useful to extend Hoffman-Berling's studies and to reestablish a permeabilized model system for investigating the mechanism of furrow constriction .…”

Polyamine‐Induced Actin Polymerization

“…Alternatively, it could also be thought that polyamines might play a role in the growth process by acting on a protein essential for cell division. Recently, Sanger [12,13] has demonstrated that actin is localized in chromosomal spindle fibers and that its localization changes during cell division. These observations led us to investigate the action of polyamines on actin.…”