title: How do amoebae swim and crawl?
abstract: The surface behaviour of swimming amoebae was followed in cells bearing a cAR1-paGFP (cyclic AMP receptor fused to a photoactivatable-GFP) construct. Sensitized amoebae were placed in a buoyant medium where they could swim toward a chemoattractant cAMP source. paGFP, activated at the cell's front, remained fairly stationary in the cell's frame as the cell advanced; the label was not swept rearwards. Similar experiments with chemotaxing cells attached to a substratum gave the same result. Furthermore, if the region around a lateral projection near a crawling cell's front is marked, the projection and the labelled cAR1 behave differently. The label spreads by diffusion but otherwise remains stationary in the cell's frame; the lateral projection moves rearwards on the cell (remaining stationary with respect to the substrate), so that it ends up outside the labelled region. Furthermore, as cAR1-GFP cells move, they occasionally do so in a remarkably straight line; this suggests they do not need to snake to move on a substratum. Previously, we suggested that the surface membrane of a moving amoeba flows from front to rear as part of a polarised membrane trafficking cycle. This could explain how swimming amoebae are able to exert a force against the medium. Our present results indicate that, in amoebae, the suggested surface flow does not exist: this implies that they swim by shape changes.
authors.affiliation: Cell Biology Division, Medical Research Council Laboratory of Molecular Biology, Cambridge, Cambridgeshire, United Kingdom.
authors.forename: Jonathan D
authors.initials: JD
authors.lastname: Howe
authors.forename: Nicholas P
authors.initials: NP
authors.lastname: Barry
authors.forename: Mark S
authors.initials: MS
authors.lastname: Bretscher
mesh_terms: D002630:Chemotactic Factors; D002633:Chemotaxis / Q000502:physiology*; D000242:Cyclic AMP / Q000378:metabolism; D004023:Dictyostelium / Q000502:physiology* / Q000648:ultrastructure; D004058:Diffusion; D015870:Gene Expression; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D008124:Locomotion / Q000502:physiology*; D008856:Microscopy, Fluorescence; D011953:Receptors, Cyclic AMP / Q000235:genetics / Q000378:metabolism; D014741:Video Recording
chemical_list: D002630:Chemotactic Factors; D011953:Receptors, Cyclic AMP; D049452:Green Fluorescent Proteins; D000242:Cyclic AMP
references.citation: Curr Biol. 2003 Sep 16;13(18):1636-40
references.pmid: 13678596
references.citation: J Cell Biol. 1994 Jun;125(6):1265-74
references.pmid: 7515888
references.citation: Mol Biol Cell. 1999 Dec;10(12):4419-27
references.pmid: 10588667
references.citation: Exp Cell Res. 1999 May 1;248(2):552-6
references.pmid: 10222146
references.citation: Science. 2001 Oct 26;294(5543):864-7
references.pmid: 11679673
references.citation: Proc Natl Acad Sci U S A. 2010 Jun 22;107(25):11376-80
references.pmid: 20534502
references.citation: J Cell Sci. 2007 Jul 15;120(Pt 14):2318-27
references.pmid: 17606987
references.citation: EMBO J. 1983;2(4):599-603
references.pmid: 6138252
references.citation: Proc Natl Acad Sci U S A. 1983 Jan;80(2):454-8
references.pmid: 6300844