Actin-based motility in the net slime mould Labyrinthula: evidence for the role of myosin in gliding movement.
In contrast to crawling movement (e.g. in amoebae and tissue cells) the other major class of substratum-associated motility in eukaryotes, gliding, has received relatively little attention. The net slime mold Labyrinthula provides a useful laboratory model for studying this process since it exhibits a particular kind of gliding in its plasmodial stage. Here nucleated spindle cells glide along self-established cytoplasmic trackways in a predominantly unidirectional manner, at 1-2 microm/s. These trackways, upon which gliding is dependent, are held by filopodial tethers some distance off the well-developed reticulopodial mesh anchoring the plasmodium onto the substratum. Reflection interference microscopy resolves this matrix in live plasmodia. The axially disposed cytoskeletal elements of the trackways are revealed by rhodamine-labelled phalloidin to be rich in F-actin. A weft of peripheral, rapidly extending filopodia (50 microm/min) typifies the expanding regions of the plasmodium. Here spindle cells are recruited before emigrating into newly differentiated trackways. Immunoblotting whole plasmodia or a sucrose-soluble cytoplasmic extract reveals a single actin-positive band of Mr 48 kDa. Polyclonal antibodies to two distinct myosin peptide sequences identify a single myosin HC (Mr 96 kDa) in immunoblots. Gliding was reversibly blocked by 10 mM 2,3-butanedione-2-monoxime, a myosin ATPase inhibitor, but it was insensitive to the actin-binding drugs cytochalasin D and phalloidin. We suggest that the force (>50 pN) for gliding motility results from interaction of myosin molecules, associated with the spindle cells, with trackway F-actin via the bothrosomes.
Preston
Terence M
TM
Biology Department, University College London, Gower Street, WC1E 6BT, United Kingdom. t.preston@ucl.ac.uk
King
Conrad A
CA
D000199:Actins / Q000378:metabolism*; D000818:Animals; D003593:Cytoplasm / Q000378:metabolism; D056890:Eukaryota / Q000254:growth & development / Q000502:physiology* / Q000648:ultrastructure; D008855:Microscopy, Electron, Scanning; D009068:Movement / Q000502:physiology*; D009218:Myosins / Q000378:metabolism*; D010935:Plant Diseases / Q000469:parasitology; D018515:Plant Leaves / Q000469:parasitology; D006109:Poaceae / Q000469:parasitology
D000199:Actins; D009218:Myosins