dictyNews
Electronic Edition
Volume 32, number 5
February 20, 2009

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Abstracts
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Review: A Novel Function of Ethylene

Aiko Amagai

Department of Biomolecular Science, Graduate School of Life Sciences,
Tohoku University, Katahira 2-1-1, Aoba-Ku, Sendai 980-8577, Japan


Gene Regulation and Systems Biology, in press

The cellular slime mold, Dictyostelium mucoroides-7 (Dm7) exhibits clear
dimorphism; macrocyst formation as a sexual process and sorocap  
formation
as an asexual process. These two life cycles are regulated by two  
regulators,
ethylene and cyclic AMP (cAMP). This is the first report demonstrating a
novel function of ethylene at the cellular level. That is, ethylene  
induces
a zygote formed by cell fusion and subsequent nuclear fusion.  
Recently, the
function of ethylene at the molecular level has been clarified as it  
induces
zygote formation through an enhanced expression of a novel gene, zyg1.
The signaling pathway for induction or inhibition of zygote formation is
now trying to be clarified focusing on the ZYG1 protein.


Submitted by: Aiko Amagai [[log in to unmask]]
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Regulation of Dictyostelium morphogenesis by RapGAP3

Taeck J. Jeon, Susan Lee, Gerald Weeks, Richard A. Firtel


Developmental Biology, in press

Rap1 is a key regulator of cell adhesion and cell motility in  
Dictyostelium.
Here, we identify a Rap1-specific GAP protein (RapGAP3) and provide
evidence that Rap1 signaling regulates cell-cell adhesion and cell  
migration
within the multicellular organism.  RapGAP3 mediates the deactivation  
of Rap1
  at the late mound stage of development and plays an important role  
in regulating
cell sorting during apical tip formation, when the anterior-posterior  
axis of the
organism is formed, by controlling cell-cell adhesion and cell  
migration. The
loss of RapGAP3 results in a severely altered morphogenesis of the  
multicellular
organism at the late mound stage.  Direct measurement of cell motility  
within
the mound shows that rapGAP3- cells have a reduced speed of movement  
and,
compared to wild-type cells, have a reduced motility towards the apex.
rapGAP3- cells exhibit some increased EDTA/EGTA sensitive cell-cell  
adhesion
at the late mound stage.  RapGAP3 transiently and rapidly translocates  
to
the cell cortex in response to chemoattractant stimulation, which is  
dependent
on F-actin polymerization.  We suggest that the altered morphogenesis  
and the
cell-sorting defect of rapGAP3- cells may result a reduced directional  
movement
of the mutant cells to the apex of the mound.


Submitted by: Rick Firtel [[log in to unmask]]
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Targeting the actin-binding protein VASP to late endosomes induces the  
formation
of giant actin aggregates

Christian Schmauch, Susan Claussner, Hellmuth Zoeltzer, and Markus  
Maniak
Abteilung Zellbiologie und CINSaT, Universitaet Kassel, Heinrich-Plett- 
Str. 40,
34132 Kassel, Germany


Eur. J. Cell Biol., in press

In vitro, the vasodilator-stimulated phosphoprotein (VASP) acts as a  
regulator
of actin filament assembly in many ways. In cells it localizes to  
sites where
actin is rapidly polymerized such as filopodia, lamellipodia, and  
focal adhesions.
We have mistargeted VASP to the surface of the late endosome in  
Dictyostelium
cells thereby inducing the formation of a dense actin aggregate which  
sequesters
various actin-binding proteins and endosomal components. Depletion of  
these
proteins from the cytoplasm leads to phenotypes mimicking the  
corresponding
knockout cells. Some properties of the actin aggregate are reminiscent  
of Hirano
bodies that are often observed in nerve tissue from patients suffering  
from
neurodegenerative diseases, opening the possibility that protein  
sequestration
contributes to neuronal malfunction.


Submitted by: Markus Maniak [[log in to unmask]]
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[End dictyNews, volume 32, number 5]