dictyNews
Electronic Edition
Volume 37, number 11
November 4, 2011

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Abstracts
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Dynamin A, Myosin IB and Abp1 couple phagosome maturation to 
F-actin binding

Navin Gopaldass, Devang Patel, Ramona Kratzke, Regis Dieckmann, 
Stéphanie Hausherr, Monica Hagedorn, Roger Monroy, Julia Krüger, 
Eva M. Neuhaus, Eik Hoffmann, Katja Hille, Sergei A. Kuznetsov and 
Thierry Soldati


Traffic, in press

The role of actin, class I myosins and dynamin in endocytic uptake processes 
is well characterized, but their role during endo-phagosomal membrane 
trafficking and maturation is less clear. In Dictyostelium, knock out of Myosin IB
leads to a defect in membrane protein recycling from endosomes back to the 
plasma membrane. Here, we show that actin plays a central role in the 
morphology and function of the endocytic pathway. Indeed, Latrunculin B 
induces endosome tubulation, a phenotype also observed in dynamin A-null 
cells. Knock out of Dynamin A impairs phagosome acidification whereas knock 
out of Myosin IB delays re-neutralisation, a phenotype mimicked by a low dose 
of Latrunculin B. As a read out for actin-dependent processes during maturation, 
we monitored the capacity of purified phagosomes to bind F-actin in vitro, and 
correlated this with the presence of actin-binding and membrane trafficking 
proteins. Phagosomes isolated from myoB-null cells showed increased binding 
to F-actin, especially late phagosomes. In contrast, early phagosome from 
dymA-null cells showed reduced binding to F-actin while late phagosomes were 
unaffected. We provide evidence that Abp1 is the main F-actin binding protein 
in this assay and is central for the interplay between Dynamin A and Myosin IB 
during phagosome maturation. 


Submitted by Thierry Soldati [[log in to unmask]]
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Amoeboid cells use protrusions for walking, gliding and swimming

Peter J.M. Van Haastert 

Department of Cell Biochemistry, University of Groningen,
Nijenborg 7, 9747AG Groningen, The Netherlands


PLoS One, in press

Amoeboid cells crawl using pseudopods, which are convex extensions 
of the cell surface. In many laboratory experiments, cells move on a smooth 
substrate, but in the wild cells may experience obstacles of other cells or 
dead material, or may even move in liquid. To understand how cells cope 
with heterogeneous environments we have investigated the pseudopod life 
cycle of wild type and mutant cells moving on a substrate and when 
suspended  in liquid. We show that the same pseudopod cycle can provide 
three types of movement that we address as walking, gliding and swimming. 
In walking the extending pseudopod will adhere firmly to the substrate, which 
allows cells to generate forces to bypass obstacles. Mutant cells with 
compromised adhesion can move much faster than wild type cells on a 
smooth substrate (gliding), but can not move effectively against obstacles 
that provide resistance. In a liquid, when swimming, the extending pseudopods 
convert to side-bumps that move rapidly to the rear of the cells. Calculations 
suggest that these bumps provide sufficient drag force to mediate the observed 
forward swimming of the cell. 


Submitted by Peter Van Haastert [[log in to unmask]]
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[End dictyNews, volume 37, number 11]