CSM News
Electronic Edition
Volume 4, number 19
May 27, 1995

Please submit abstracts of your papers as soon as they have been
accepted for publication by sending them to CSM-News@worms.cmsbio.nwu.edu.

Back issues of CSM-News, the CSM Reference database and other useful
information is available by anonymous ftp from worms.cmsbio.nwu.edu
[165.124.233.50], via Gopher at the same address, or by World Wide Web
at the URL "http://worms.cmsbio.nwu.edu/dicty.html"

===========
 Abstracts
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Cell-cycle progression during the development of Dictyostelium
discoideum and its relation to the subsequent cell-sorting in the
multicellular structures

Tsuyoshi Araki and Yasuo Maeda

Biological Institute, Faculty of Science, Tohoku University, Aoba,
Sendai 980-77, JAPAN

Development Growth and Differentiation, in press

ABSTRACT

   Previous studies have shown that the cell-cycle phase at the onset
of starvation is a naturally-occurring variable that is closely
involved in the subsequent sorting and differentiation of cells during
Dictyostelium development. Here the cell-cycle progression during the
development of D.  discoideum Ax-2 cells and its relation to the
subsequent cell-sorting were analyzed in detail using synchronized
cells and their pulse-labeling by 5'-bromodeoxyuridine
(BrdU). Measurements of cell number and nuclearity provided evidence
that about 80% of cells progressed their cell-cycle after formation of
multicellular structures (mounds). Many of cells (T7 cells) starved at
mid-late G2-phase (just before the PS-point from which cells initiate
development when starved) progressed the cell-cycle after mound
formation. In contrast, a fewer number of cells (T1 cells) starved at
late G2-phase (just after the PS-point) progressed the cell-cycle
after mound formation. The significance of cell-cycle progression
presented here is discussed, with reference to cell differentiation
and pattern formation.

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The G protein beta-subunit is essential for multiple responses to
chemoattractants in Dictyostelium

Lijun Wu*@,  Romi Valkema +,  Peter J.M.Van Haastert+, and 
Peter N. Devreotes*++

*Dept. of Biological Chemistry, Johns Hopkins University, School of
Medicine Baltimore, MD 21205 + Dept. of Biochemistry, University of
Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands, @ Present
Address: LeukoSite, Inc., 215 First Street, Cambridge, MA 02142

J. Cell Biol., in press.

ABSTRACT
	
   Increasing evidence suggests that the bg-subunit dimers of
heterotrimeric G proteins play a pivotal role in transducing
extracellular signals.  The recent construction of Gb null mutants
(gb-) in Dictyostelium provides a unique opportunity to study the role
of bg-dimers in signaling processes mediated by chemoattractant
receptors.  We have shown previously that gb- cells fail to aggregate;
in this study, we report the detailed characterization of these cells.
The gb- cells display normal motility but do not move towards
chemoattractants.  The typical GTP-regulated high affinity
chemoattractant binding sites are also lost in gb- cells and
membranes.  The gb- cells do not display chemoatrractant-stimulated
adenylyl cyclase or guanylyl cyclase activity.  These results show
that in vivo Gb links chemoattractant receptors to effectors and is
therefore essential in many chemoattractant-mediated processes.  In
addition, we find that Gb is required for GTPgS stimulation of
adenylyl cyclase activity, suggesting that it activates the enzyme
directly.  Interestingly, the gb- cells grow at the same rate as
wild-type cells in axenic medium but grow more slowly on bacterial
lawns and, therefore, may be defective in phagocytosis.

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[End CSM News, volume 4, number 19]