Investigation of the mechanism of retraction of the cell margin and rearward flow of nodules during mitotic cell rounding.

Abstract

We have studied two types of cell motility directed toward the cell center: retraction of the cell margin and rearward flow of small cytoplasmic nodules during mitotic cell rounding in Potoroo tridactylis kidney (PtK2) cells by time-lapse video microscopy, drug treatments, and photoactivation of fluorescence. Nodules flow rearward on thin, actinrich fibers (retraction fibers) exposed as the cell margin retracts. Retraction of the cell margin and rearward flow of nodules require intact actin filaments, but are insensitive to an inhibitor of myosin function (butanedione monoxime). Using photoactivation of fluorescence marking, we have determined that actin filaments in the majority of retraction fibers remain stationary while the cell margin retracts and nodules flow rearward. The pointed ends of retraction fiber actin filaments face the cell center. We argue that nodule motility is driven by a novel actin-based force that perhaps also partially contributes to retraction of the cell margin during cell rounding at mitosis.

The metastatic cancer cell cortex: An adaptation to enhance robust cell division in novel environments?

“…As adherent cells round up upon entry into mitosis, they maintain attachment to this underlying substrate through actin-rich retraction fibers [6]. This integrin-mediated attachment to the ECM has been shown to guide spindle positioning [7,8].…”

“…When adherent cells enter mitosis, they partially detach from the substrate, retract their margin, and round up to form a sphere [6]. Similarly, cells round up and push aside their neighbors as they enter mitosis when dividing in the context of a crowded epithelium [14,15].…”

Epithelial cell division in the Xenopus laevis embryo during gastrulation

“…For example, when they enter mitosis, in vitro cultured cells undergo remarkable shape changes. Contacts of the mitotic cells with the substratum are usually attenuated and cells round up dramatically (Cramer andMitchison, 1997, Maddox andBurridge, 2003). In intact tissues, such as epithelium, in which cell-cell contacts are tight, modifications of the mitotic cell shape still occur.…”

Diffusion, capture and recycling of SCAR/WAVE and Arp2/3 complexes observed in cells by single-molecule imaging

“…Retrograde flow was first visualized with techniques such as FRAP and photoactivation (Wang, 1985;Theriot and Mitchison, 1991;Theriot and Mitchison, 1992;Lin and Forscher, 1995;Cramer and Mitchison, 1997). Because data from these techniques can hide local differences in actin assembly, researchers have recently used additional methods such as single-molecule and speckle microscopy to analyze the fine-grained spatial and temporal dynamics of actin rearrangements (Watanabe and Mitchison, 2002;Ponti et al, 2004).…”