Copy Link
Add to Bookmark
Report
dictyNews Volume 31 Number 05
dictyNews
Electronic Edition
Volume 31, number 5
Aug 1, 2008
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.
Upon publication of your paper, please send strains and plamids to
the Dicty Stock Center. For more information see
http://dictybase.org/StockCenter/Deposit.html.
Back issues of dictyNews, the Dicty Reference database and other
useful information is available at dictyBase - http://dictybase.org.
=========
Abstracts
=========
A Protein with Similarity to PTEN Regulates Aggregation Territory Size
by Decreasing cAMP Pulse Size during Dictyostelium Development
Yitai Tang and Richard H. Gomer*
Department of Biochemistry and Cell Biology, Rice University, Houston, Texas
Eukaryotic Cell, in press
An interesting but largely unanswered biological question is how eukaryotic
organisms regulate the size of multicellular tissues. During development,
a lawn of Dictyostelium cells breaks up into territories, and within the
territories the cells aggregate in dendritic streams to form groups of
~20,000 cells. Using random insertional mutagenesis to search for genes
involved in group size regulation, we found that an insertion in the cnrN
gene affects group size. Cells lacking CnrN (cnrN–) form abnormally small
groups, which can be rescued by the expression of exogenous CnrN. Relayed
pulses of extracellular adenosine 3’5’-cyclic monophosphate (cAMP) direct
cells to aggregate by chemotaxis to form aggregation territories and
streams. cnrN– cells over-accumulate cAMP during development and form
small territories. Decreasing the cAMP pulse size by treating cnrN– cells
with cAMP phosphodiesterase (PDE) or starving cnrN– cells at a low density
rescues the small territory phenotype. The predicted CnrN sequence has
similarity to phosphatase and tensin homolog (PTEN), which in Dictyostelium
inhibits cAMP-stimulated phosphatidylinositol 3’ kinase (PI3K) signaling
pathways. CnrN inhibits cAMP-stimulated PIP3 accumulation, Akt activation,
actin polymerization, and cAMP production. Our results suggest that CnrN
is a protein with some similarities to PTEN, and regulates cAMP signal
transduction to regulate territory size.
Submitted by: Yitai Tang [yttang@rice.edu]
--------------------------------------------------------------------------------
Dictyostelium myosin-5b is a conditional processive motor
Manuel H. Taft, Falk K. Hartmann, Agrani Rump, Heiko Keller, Igor Chizhov,
Dietmar J. Manstein, and Georgios Tsiavaliaris
Institute for Biophysical Chemistry, Hannover Medical School,
Hannover D-30625
Corresponding Author: gtsiaval@bpc.mh-hannover.de
JBC, in press
Dictyostelium myosin-5b is the gene product of myoJ and one of two closely
related myosin-5 isoenzymes produced in Dictyostelium discoideum. Here
we report a detailed investigation of the protein’s kinetic and functional
properties. In standard assay buffer conditions, Dictyostelium myosin-5b
displays high actin affinity in the presence of ADP, fast ATP hydrolysis,
and a high steady-state ATPase activity in the presence of actin that is
rate limited by ADP release. These properties are typical for a processive
motor that can move over long distances along actin filaments without
dissociating. Our results show that a physiological decrease in the
concentration of free Mg2+-ions leads to an increased rate of ADP release
and shortening of the fraction of time the motor spends in the strong
actin binding states. Consistently, the ability of the motor to efficiently
translocate actin filaments at very low surface densities decreases with
decreasing concentrations of free Mg2+-ions. In addition, we provide
evidence that the observed changes in Dd myosin-5b motor activity are of
physiological relevance and propose a mechanism by which this molecular
motor can switch between processive and non-processive movement.
Submitted by: Georgios Tsiavaliaris [gtsiaval@bpc.mh-hannover.de]
--------------------------------------------------------------------------------
A Dictyostelium homologue of the metazoan Cbl proteins regulates STAT
signalling
(Dictyostelium Cbl and STAT regulation)
Judith Langenick, Tsuyoshi Araki, Yoko Yamada and Jeffrey G. Williams+
University of Dundee, School of Life Sciences, Dow Street, Dundee DD1
5EH , UK
J Cell Sci, in press
Cbl proteins down-regulate metazoan signalling pathways by ubiquitylating
receptor tyrosine kinases, thereby targeting them for degradation. They
contain a phosphotyrosine-binding region, comprised of an EF-hand and an
SH2 domain, linked to an E3 ubiquitin-ligase domain. CblA, a Dictyostelium
homologue of the Cbl proteins, contains all three conserved domains. In a
cblA- strain early development occurs normally but migrating cblA- slugs
frequently fragment and the basal disc of the culminants that are formed
are absent or much reduced. These are characteristic features of mutants
in signalling by DIF-1: the low molecular weight, prestalk and stalk cell
inducer. Tyrosine phosphorylation of STATc is induced by DIF-1 but in the
cblA- strain this response is attenuated relative to parental cells. We
present evidence that CblA fulfils this function, as a positive regulator
of STATc tyrosine phosphorylation, by down-regulating PTP3: the protein
tyrosine phosphatase responsible for de-phosphorylating STATc. Thus Cbl
proteins have an ancient origin but, while metazoan Cbl proteins regulate
tyrosine kinases, the Dictyostelium Cbl regulates via a a tyrosine
phosphatase.
Submitted by: Jeff Williams [j.g.williams@dundee.ac.uk]
==============================================================
[End dictyNews, volume 31, number 5]
