dictyNews
Electronic Edition
Volume 40, number 19
August 8, 2014

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=========
Abstracts
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TITLE: Comparison of Dictyostelium LvsB and endosomal fission defect 
mutants support a fusion regulatory role for LvsB

AUTHORS: Kristin Falkenstein and Arturo De Lozanne
Section of Molecular Cell & Developmental Biology
and Institute for Cellular and Molecular Biology,
University of Texas at Austin, Austin, TX 78712.


JOURNAL: Journal of Cell Science

ABSTRACT: Defects in human Lyst are associated with the lysosomal 
disorder Chediak Higashi Syndrome.  The absence of Lyst results in 
the formation of enlarged lysosome related compartments but the 
mechanism for how these compartments arise is not well established.  
Two opposing models have been proposed to explain Lyst function.  
The fission model describes Lyst as a positive regulator of fission 
from lysosomal compartments, while the fusion model identifies Lyst 
as a negative regulator of fusion between lysosomal vesicles. Here 
we used assays that can distinguish between defects in vesicle fusion 
versus fission. We compared the phenotype of Dictyostelium cells 
defective in LvsB, the ortholog of Lyst, with that of two known fission 
defect mutants (΅3 and WASH null mutants).  We found that the temporal 
localization characteristics of the post-lysosomal marker vacuolin, as 
well as vesicular acidity and fusion dynamics of LvsB null cells are 
distinct from those of both ΅3 and WASH null fission defect mutants.  
These distinctions are predicted by the fusion defect model and 
implicate LvsB as a negative regulator of vesicle fusion.

Submitted by Arturo De Lozanne [a.delozanne@utexas.edu]
ΡΡΡΡΡΡΡΡΡΡΡΡΡΡΡΡΡΡΡΡΡΡΡΡΡΡΡΡΡΡΡΡΡΡΡ


A simple optical configuration for cell tracking by dark-field 
microscopy

Vlatka Antolovic, Maja Marinovic, Vedrana Filic, Igor Weber


Journal of Microbiological Methods  (2014), pp. 9-11
DOI information: 10.1016/j.mimet.2014.06.006
http://authors.elsevier.com/a/1PT8Kc8NxIVdE 
(free download until September 21, 2014)

We describe a simple optical configuration for dark-field microscopy 
at low magnification, realized with the use of standard microscope 
components. An inherent high contrast makes this method attractive 
for computer-assisted tracking and counting of microorganisms. We 
applied this setup for dark-field microscopy to measure the speed 
of migrating Dictyostelium amoebae.

Submitted by Vedrana Filic [vedrana.filic@irb.hr]
ΡΡΡΡΡΡΡΡΡΡΡΡΡΡΡΡΡΡΡΡΡΡΡΡΡΡΡ


Actin and PIP3 waves in giant cells reveal the inherent length 
scale of an excited state

Matthias Gerhardt, Mary Ecke, Michael Walz, Andreas Stengl, Carsten Beta, 
and GŸnther Gerisch


Journal of Cell Science, accepted

The membrane and actin cortex of a motile cell can autonomously 
differentiate into two states, one typical of the front, the other of 
the tail. On the substrate-attached surface of Dictyostelium cells, 
dynamic patterns of front-like and tail-like states are generated that 
are best suited to monitor transitions between these states. To image 
large-scale pattern dynamics independent of boundary effects, we produced 
giant cells by electric-pulse induced cell fusion. In these cells actin 
waves are coupled to the front and back of PIP3-rich bands that have a 
finite width. These composite waves propagate across the plasma membrane 
of the giant cells with undiminished velocity. After any disturbance, the 
bands of PIP3 return to their intrinsic width. Upon collision, the waves 
locally annihilate each other and change direction; at the cell border 
they are either extinguished or reflected. Accordingly, expanding areas of 
progressing PIP3 synthesis become unstable beyond a critical radius, their 
center switching from a front-like to a tail-like state. Our data suggest 
that PIP3 patterns in normal-sized cells are segments of the self-organizing 
patterns that evolve in giant cells.

Submitted by GŸnther Gerisch [gerisch@biochem.mpg.de]
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[End dictyNews, volume 40, number 19]