CSM News
Electronic Edition
Volume 2, number 14
April 16, 1994

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.

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through www.nwu.edu.

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Abstracts
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Regulation of myosin regulatory light chain phosphorylation via cyclic
GMP during chemotaxis of Dictyostelium

Gang Liu and Peter C. Newell

Department of Biochemistry, University of Oxford, South Parks Road,
Oxford OX1 3QU, UK

J. Cell Sci., in press

	Previous studies on chemotactic movement of Dictyostelium have
indicated a role for cyclic GMP in regulating association of myosin II
with the cytoskeleton.  In this study we have examined the part played
by phosphorylation of the 18 KDa myosin regulatory light chain in this
event.  Using streamer F mutant NP368 (which is deficient in the
structural gene for cyclic GMP-specific phosphodiesterase) we find
that, for the regulatory light chain kinase, the major peak of
phosphorylation is delayed compared to the parental control strain
XP55, occurring at 80 sec rather than about 30 sec in XP55.  In two
independently-derived mutants that are unable to increase their
cellular concentration of cyclic GMP (above basal levels) in response
to a chemotactic stimulus of cyclic AMP (KI-10 and SA219), no increase
in the phosphorylation of the light chain occurred, or movement of
myosin II to the cytoskeleton.  We also find a smaller peak of light
chain phosphorylation which occurs within 10 sec of cyclic AMP
stimulation of the amoebae and which is absent in the cyclic
GMP-unresponsive strains.  We conclude that cyclic GMP is involved in
regulating light chain phosphorylation in this system.  The
significance of this conclusion is discussed and a model is presented
that relates these findings to published data on cytoskeletal myosin
changes during chemotaxis.

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Calcium-sequestering organelles of Dictyostelium discoideum: changes in
element content during early development as measured by electron probe
X-ray microanalysis. 

Christina Schlatterer*, Sergeij Buravkov, Karl Zierold, and Gerd Knoll

Faculty of Biology, University of Konstanz, D-78434 Konstanz, FRG

Cell Calcium, in press.

   Starving Dictyostelium discoideum amoebae aggregate within a few hours
by chemotaxis towards the attractant cAMP to form a multicellular
organism.  The differentiating cells possess rapid and efficient
calcium buffering and sequestration systems which enable them to
restrict changes in the cytosolic free calcium concentration
temporally and spatially during their chemotactic reaction and allow
the continous accumulation of Ca2+ during development. In order to
identify and to characterize calcium storage compartments we analyzed
the element content of amoebae at three consecutive stages of
differentiation. Determination of the element distribution was done
using energy-dispersive X-ray microanalysis of freeze-dried
cryosections of rapid-frozen cells.  Amoebae were frozen in the
vegetative and aggregation-competent state and after formation of
aggregates. Aggregation-competent as well as aggregated cells
contained mass dense granules with large amounts of calcium together
with phosphorous and either potassium or magnesium: in
aggregation-competent cells calcium was colocalized with potassium,
whereas in aggregated cells the mass dense granules contained calcium
and magnesium. Although mass dense granules were also present in
undifferentiated, vegetative cells, they contained only low amounts of
phosphorous and potassium together with little Ca and Mg. We conclude
that during their differentiation D. discoideum cells use an
intracellular storage compartment to sequester Ca and other cations
constantly throughout development.

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[End CSM News, volume 2, number 14]