title: Reconstitution of amoeboid motility in vitro identifies a motor-independent mechanism for cell body retraction.
abstract: Crawling movement in eukaryotic cells requires coordination of leading-edge protrusion with cell body retraction [1-3]. Protrusion is driven by actin polymerization along the leading edge [4]. The mechanism of retraction is less clear; myosin contractility may be involved in some cells [5] but is not essential in others [6-9]. In Ascaris sperm, protrusion and retraction are powered by the major sperm protein (MSP) motility system instead of the conventional actin apparatus [10, 11]. These cells lack motor proteins [12] and so are well suited to explore motor-independent mechanisms of retraction. We reconstituted protrusion and retraction simultaneously in MSP filament meshworks, called fibers, that assemble behind plasma membrane-derived vesicles. Retraction is triggered by depolymerization of complete filaments in the rear of the fiber [13]. The surviving filaments reorganize to maintain their packing density. By packing fewer filaments into a smaller volume, the depolymerizing network shrinks and thereby generates sufficient force to move an attached load. Our work provides direct evidence for motor-independent retraction in the reconstituted MSP motility system of nematode sperm. This mechanism could also apply to actin-based cells and may explain reports of cells that crawl even when their myosin activity is compromised.
authors: Department of Biological Science, Florida State University, Tallahassee, FL 32306, USA.
authors: Katsuya
authors: K
authors: Shimabukuro
authors: Naoki
authors: N
authors: Noda
authors: Murray
authors: M
authors: Stewart
authors: Thomas M
authors: TM
authors: Roberts
mesh_terms: D000818:Animals; D001200:Ascaris / Q000166:cytology*; D015801:Helminth Proteins / Q000378:metabolism*; D008297:Male; D013081:Sperm Motility; D013094:Spermatozoa / Q000166:cytology* / Q000000981:diagnostic imaging / Q000378:metabolism; D014463:Ultrasonography
chemical_list: D015801:Helminth Proteins; C050602:major sperm protein, nematode