Dicty News
Electronic Edition
Volume 24, number 11
April 22, 2005

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


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  Abstracts
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Peptide signaling during terminal differentiation of Dictyostelium

Christophe Anjard and William F. Loomis
Center for Molecular Genetics, Division of Biological Sciences,
University of California San Diego, La Jolla, CA 92093-0368


Proc. Natl. Acad. Sci. USA, in press

A wide variety of mechanisms have evolved for intercellular communication
in metazoans but some of the signaling molecules were already used in their
predecessors. The social amoeba, Dictyostelium discoideum, is known to use
peptides to trigger sporulation within fruiting bodies but their sequences
have not been defined. We found that the peptide signal SDF-2 is processed
from acyl-CoA binding protein, AcbA. The mammalian homolog of AcbA is
processed to DBI (Diazepam Binding Inhibitor) that binds to the GABAA
receptor in the brain and to peripheral 1,4 benzodiazepine receptors (PBR).
Although Dictyostelium has neither GABAA nor peripheral-type benzodiazepine
receptors, we find that both a DBI peptide and diazepam (Valium) can mimic
SDF-2 in a Dictyostelium bioassay.  Mutants lacking AcbA sporulate well only
when developed in chimeras with wild type cells. Using a yeast system we
show that ligand binding to the SDF-2 receptor histidine kinase, DhkA,
inhibits phosphorelay which can account for its ability to induce rapid
sporulation.


Submitted by: William F. Loomis [wloomis@ucsd.edu]

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Pushing Forces Drive the Comet-Like Motility of Microtubule Arrays in
Dictyostelium

D.A. Brito, J. Strauss, V. Magidson, I. Tikhonenko, A.Khodjakov, and
M. P. Koonce

Division of Molecular Medicine
Wadsworth Center
Albany, NY, 12201-0509


Molecular Biology  of the Cell, in press

Overexpression of dynein fragments in Dictyostelium induces the movement
of the entire interphase microtubule array. Centrosomes in these cells
circulate through the cytoplasm at rates between 0.4 and 2.5 _m/sec, and
are trailed by a comet-tail like arrangement of the microtubule array.
Previous work suggested that these cells use a dynein-mediated pulling
mechanism to generate this dramatic movement, and that similar forces are
at work to maintain the interphase MTOC position in wild type cells. In the
present study, we address the nature of the forces used to produce
microtubule movement. We have used a laser microbeam to sever the connection
between the motile centrosomes and trailing microtubules, demonstrating that
the major force for such motility results from a pushing on the microtubules.
We eliminate the possibility that microtubule assembly/disassembly reactions
are significant contributors to this motility, and suggest that the cell
cortex figures prominently in locating force-producing molecules. Our
findings indicate that interphase microtubules in Dictyostelium are subject
to both dynein and kinesin-like forces, and that these act in concert to
maintain centrosome position in the cell and to support the radial character
of the microtubule network.


Submitted by: Michael Koonce [koonce@wadsworth.org]

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[End Dicty News, volume 24, number 11]