dictyNews
Electronic Edition
Volume 26, number 7
March 3, 2006

Please submit abstracts of your papers as soon as they have been
accepted for publication by sending them to dicty@northwestern.edu
or by using the form at
http://dictybase.org/db/cgi-bin/dictyBase/abstract_submit.

Back issues of dictyNews, the Dicty Reference database and other 
useful information is available at dictyBase - http://dictybase.org.


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  Abstracts
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Migration in Dictyostelium polycephalum
J. T. Bonner

Department of Ecology and Evolutionary Biology, Princeton University, 
Princeton, NJ 08544


Mycologia, in press

By comparing two species of cellular slime molds that have a stalkless 
migration stage, it is possible to gain some interesting new insights into 
how the cell masses move.  In contrast to the well known behavior of 
Dictyostelium discoideum, the slugs of Dictyostelium polycephalum can 
travel greater distances through soil and can even migrate through agar.  
Besides the intrinsic interest of the differences, they shed light on the 
mechanism of slug movement.  Unlike D. discoideum, D. polycephalum does not 
have prestalk and prespore zones, and severed sections of any part of their 
slugs move at a rate proportional to their length.  This leads to the 
hypothesis that longer slugs move faster because in the extended column of 
amoebae each one contributes a forward push, and the longer the line of 
these amoebae the faster the slug moves.  


Submitted by: John Bonner [jtbonner@princeton.edu]
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A small GTPase RacF2 affects sexual cell fusion and asexual development in 
Dictyostelium discoideum through the regulation of cell adhesion


Tetsuya Muramoto and Hideko Urushihara

Develop. Growth Differ., in press.

Cells of Dictyostelium discoideum become sexually mature when submerged and 
in darkness, and fuse with opposite mating-type cells as gametes. The gene 
for a Rho GTPase, RacF2, is one of the extremely gamete-enriched genes 
(>100-fold) identified by us previously. Here, we isolated knockout, 
overexpression, constitutively active and dominant negative mutants of 
RacF2, and analyzed their phenotypes. These mutants showed anomalies in the 
extent of sexual cell fusion and asexual development as well as in 
EDTA-sensitive cell-cell adhesion. It is suggested that RacF2 controls the 
process of sexual and asexual development through the regulation of cellular 
adhesiveness. An analysis of the expression of all 18 rac family genes by 
real-time polymerase chain reaction revealed that four additional genes, 
rac1b, rac1c, racF1 and racG, were induced during maturation, suggesting 
their possible involvement in sexual cell interactions. 


Submitted by: Hideko Urushihara [hideko@biol.tsukuba.ac.jp]
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Nap1 Regulates Dictyostelium Cell Motility and Adhesion Through SCAR 
Dependent and Independent Pathways

Neysi Ibarra, Simone L. Blagg, Francisca Vazquez~ and Robert H. Insall*


Current Biology, in press

SCAR Ð also known as WAVE - is a key regulator of actin dynamics.
Activation of SCAR enhances the nucleation of new actin filaments through
the Arp2/3 complex, causing a localised increase in the rate of actin
polymerization. In vivo, SCAR is held in a large regulatory complex, which
includes PIR121 and Nap1 proteins, whose precise role is unclear. It was
initially thought to hold SCAR inactive until needed, but recent data
suggest that it is essential for SCAR function. Here we show that
disruption of the gene that encodes Nap1 (napA) causes loss of SCAR
function. Cells lacking Nap1 are small and rounded, with diminished actin
polymerization and small pseudopods. Furthermore, several aspects of the
napA phenotype are more severe than those evoked by the absence of SCAR
alone. In particular, napA mutants have defects in cell-substrate adhesion
and multicellular development. Despite these defects, napA- cells move and
chemotax surprisingly effectively. Our results show that the members of 
the complex have unexpectedly diverse biological roles.


Submitted by: Robert H. Insall [R.H.Insall@bham.ac.uk]
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[End dictyNews, volume 26, number 7]