CSM News
Electronic Edition
Volume 4, number 16
May 6, 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.

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===========
 Abstracts
===========

Patterns of free calcium in multicellular stages of Dictyostelium  
expressing jellyfish apoaequorin 

Andrew B. Cubitt1,2, Richard A. Firtel2, Gabriele Fischer1,3, Lionel F. 
Jaffe1,*, and Andrew L. Miller1 

1 Marine Biological Laboratory, Woods Hole, Massachusetts 02543, USA
2 Department of Biology, Center for Molecular Genetics, University of 
California San Diego, La Jolla, California 92093, USA
3 Fakultat fur Biologie, Universitat Konstanz, D-78434 Konstanz, Germany
* Author for correspondence

Development, in press.

SUMMARY
   To examine the patterns of high free cytosolic calcium or [Ca2+]i
during Dictyostelium's development, we expressed apoaequorin in D.
discoideum, reconstituted aequorin and observed the resultant patterns
of calcium-dependent luminescence.  Specific, high calcium zones are
seen throughout normal multicellular development and are roughly
coincident with those regions that later differentiate into stalk or
stalk-like cells.  A slug, for example, shows a primary high calcium
zone within its front quarter and a secondary one around its tail;
while a mound shows such a zone around the periphery of its base.
Combined with previous evidence, our findings support the hypothesis
that high [Ca2+]i feeds back to favor the stalk pathway.
   
   We also discovered several high calcium zones within the mound's
base that do not coincide with any known prepatterns in D. discoideum.
These include two, relatively persistent, antipodal strips along the
mound's periphery.  These various persistent zones of high calcium are
largely made up of frequent, 10 to 30 second long, semiperiodic
calcium spikes.  Each of these spikes generates a correspondingly
short-lived, 200 to 500 microns long, high calcium band which extends
along the nearby surface.  Similar, but relatively large and
infrequent, spikes generate cross bands which extend across migrating
slugs and just behind their advancing tips as well as across the
peripheries of rotating mounds and midway between their antipodal
strips.  Moreover, calcium has a doubling time of about a second as
various spikes rise.  This last observation suggests that the calcium
bands seen in Dictyostelium may be generated by so-called fast calcium
waves.

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Capping protein levels influence actin assembly and cell motility in
Dictyostelium.

C. Hug, P. Y. Jay, I. Reddy, J. G. McNally, P. C. Bridgman, E. L.
Elson and J. A. Cooper.

Cell, in press

     Actin assembly is important for cell motility, but the mechanism
of assembly and how it relates to motility in vivo is largely unknown.
In vitro, actin assembly can be controlled by proteins, such as
capping protein, that bind filament ends. To investigate the function
of actin assembly in vivo, we altered the levels of capping protein in
Dictyostelium cells, and found changes in resting and
chemoattractant-induced actin assembly that were consistent with
capping protein's in vitro properties of capping but not nucleation.
Significantly, overexpressers moved faster and underexpressers moved
slower than control cells. Mutants also exhibited changes in
cytoskeleton architecture. These results provide new insights into in
vivo actin assembly and the actin cytoskeleton's role in motility.

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[End CSM-News, volume 4, number 16]