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SUMMARY:How filament assembly dynamics can power the crawling motion of am
 oeboid cells - Dr Murray Stewart\, MRC Laboratory of Molecular Biology\, C
 ambridge
DTSTART:20070216T141500Z
DTEND:20070216T151500Z
UID:TALK6094@talks.cam.ac.uk
CONTACT:Dr Kalin Dragnevski
DESCRIPTION:Amoeboid cells crawl by extending a pseudopod at their leading
  edge while also drawing their trailing cell body forward.  Both of these 
 processes are driven by the polymerization dynamics of the cell cytoskelet
 on\, which is composed of a meshwork of filaments that polymerize and depo
 lymerise at defined locations in the cell.  I will discuss results obtaine
 d from a simple and specialized model system that uses the sperm of the ne
 matode Ascaris to investigate the mechanisms by which filament assembly dy
 namics can power cell locomotion.  Although the nematode sperm system empl
 oys the protein MSP instead of the actin that forms the basis of motility 
 in most other cells\, its motile behaviour is very similar.  Both protrusi
 on and retraction can be reconstituted in vitro and these assays demonstra
 te that\, whereas protrusion is driven by filament assembly\, retraction i
 nvolves filament disassembly.  Although several models have been proposed 
 to account for how polymerization drives protrusion\, the precise mechanis
 m remains controversial.  I will present evidence that suggests that the w
 ay elongating filaments pack contributes substantially to this gel expansi
 on.  Tomography shows that filament packing in the nematode sperm motility
  machinery resembles that observed with rigid rods.  Maximum rod packing d
 ensity decreases dramatically as they lengthen.  Thus as filaments elongat
 e\, the cytoskeleton gel must expand to accommodate their packing less den
 sely.  This volume expansion combines with polymerization to drive protrus
 ion.  Consistent with this hypothesis\, an engineered MSP mutant that gene
 rates shorter filaments shows higher filament packing density and slower m
 ovement.  Quantitation indicates that filament packing and polymerization 
 contribute equally to the rate of protrusion in MSP fibres that produce th
 e same pattern of movement as related actin-based systems.  Actin filament
 s have similar stiffness and pack like MSP at the leading edge\, indicatin
 g that gel expansion generated by filament packing effects would also cont
 ribute to protrusion in these systems.
LOCATION:IRC in Superconductivity Seminar Room\, Cavendish Laboratory
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