Electronic Edition
Volume 38, number 9
March 30, 2012

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=========
Abstracts
=========


Cooper RM, Wingreen NS, Cox EC

An excitable cortex and memory model successfully predicts new pseudopod 
dynamics.


PLoS One available online http://dx.plos.org/10.1371/journal.pone.0033528

Motile eukaryotic cells migrate with directional persistence by alternating 
left and right turns, even in the absence of external cues.  For example, 
Dictyostelium discoideum cells crawl by extending distinct pseudopods in 
an alternating right-left pattern.  The mechanisms underlying this zig-zag 
behavior, however, remain unknown.  Here we propose a new Excitable 
Cortex and Memory (EC&M) model for understanding the alternating, 
zig-zag extension of pseudopods. Incorporating elements of previous models, 
we consider the cell cortex as an excitable system and include global inhibition 
of new pseudopods while a pseudopod is active.  With the novel hypothesis 
that pseudopod activity makes the local cortex temporarily more excitable – 
thus creating a memory of previous pseudopod locations – the model 
reproduces experimentally observed zig-zag behavior. Furthermore, the 
EC&M model makes four new predictions concerning pseudopod dynamics.  
To test these predictions we develop an algorithm that detects pseudopods 
via hierarchical clustering of individual membrane extensions.  Data from 
cell-tracking experiments agrees with all four predictions of the model, 
revealing that pseudopod placement is a non-Markovian process affected 
by the dynamics of previous pseudopods.  The model is also compatible 
with known limits of chemotactic sensitivity.  In addition to providing a 
predictive approach to studying eukaryotic cell motion, the EC&M model 
provides a general framework for future models, and suggests directions 
for new research regarding the molecular mechanisms underlying directional 
persistence.


Submitted by Robert Cooper [[log in to unmask]]
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