Keep the motor running

Abstract

The swirling movements of the centrosome and microtubules in a live Dictyostelium cell are shown in this sequence of images.this sequence of images.Sequence of images.Sequence of images.Sequence of images.Sequence of images.Sequence of images.Sequence of images.Sequence of images.Sequence of images.Sequence of images.Sequence of images.Sequence of images.Sequence of images.Sequence of images.Sequence of images.View Large Image | View Hi-Res Image | Download PowerPoint SlideSequence of images.Sequence of images.View Large Image | View Hi-Res Image | Download PowerPoint SlideSequence of images.Sequence of images.View Large Image | View Hi-Res Image | Download PowerPoint SlideSequence of images.Sequence of images.View Large Image | View Hi-Res Image | Download PowerPoint SlideSequence of images.Sequence of images.View Large Image | View Hi-Res Image | Download PowerPoint SlideSequence of images.Sequence of images.View Large Image | View Hi-Res Image | Download PowerPoint SlideSequence of images.Sequence of images.View Large Image | View Hi-Res Image | Download PowerPoint SlideThese were taken over the course of about five minutes using α-tubulin tagged with a green fluorescent protein. The movements are more frenetic than usual because the cell is a mutant that over-expresses the motor domain of the protein dynein.Dynein has several roles in eukaryotes, including moving organelles and anchoring microtubules to the cell cortex. In Dictyostelium, interphase microtubules can be uncoupled from the cortex by the overexpression of dynein motor-domain fragments. This causes the entire microtubule array to become motile in the cytoplasm; the centrosome circulates along the cell periphery, followed by loose, wavy bundles of microtubules.The mechanism for this motility may involve cortically anchored dyneins that transiently engage the microtubule array. In normal cells this activity would reinforce the radial array and maintain the central position of the centrosome, as cells crawl and change shape. In cells like the mutant one shown here, most of the cortical dynein activity seems to have been ‘turned off’; a few remaining active dyneins could pull on a microtubule and move the array, much like pulling on a single strand of a mop head in a bucket of water. A function of dynein in normal cells, therefore, is to maintain the central location of the centrosome, and a small region on the motor domain may serve as an on/off switch.See the online version of this article for a video of the movements. For details see Koonce M.P., et al, EMBO J 1999, 18:6786-6792. Images provided by Michael Koonce, Wadsworth Center, Albany, New York 12201, USA, and Ralph Neujahr, Max Planck Institut fur Biochemie, Martinsried, Germany.