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dictyNews Volume 22 Number 05
Dicty News
Electronic Edition
Volume 22, number 5
February 27, 2004
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.
====================
Special Announcement
====================
I just want to say hello and goodbye to all colleagues now that I have
retired from the fray. Thanks to all of you for friendship, help,
encouragement, criticism, and competition, over the years. Hope to see you
some time, though where, when and how I donât know. I now have my home
address and email on the website and would appreciate receiving news
and reprints.
Julian Gross
=============
Abstracts
=============
Dynamics of novel feet of Dictyostelium cells during migration
Authors: Kazuhiko S. K. Uchida (1) and Shigehiko Yumura (Author for
correspondence)(2)
(1) Present address: Institute of Biological Sciences, University of Tsukuba,
Tsukuba, Ibaraki 305-8572, Japan
(2) Department of Biology, Faculty of Science, Yamaguchi University, Yamaguchi
753-8512, Japan
Journal of Cell Science, in press
We observed the dynamics of actin foci in live Dictyostelium cells expressing
GFP-actin. Actin foci were dynamic structures, but they were fixed on the
substratum during cell migration. Interference reflection microscopy revealed
that the ventral cell membrane was closer to the substratum at sites of actin
foci. Furthermore, some actin foci were incorporated into the retraction
fibers, ripped off from the cells, and eventually shed on the substratum after
the cells moved away. The velocity of the cells was inversely proportional to
the number of actin foci. Measurement of traction force using a silicone
substratum demonstrated that the traction force was transmitted to the
substratum through actin foci. Taken together, several lines of evidence
strongly suggest that actin foci function as the active 'feet' of
Dictyostelium cells. We also found evidence suggesting that these changing
steps are regulated in a coordinated manner during cell migration. Possible
mechanisms by which these cells migrate across substrata are discussed in
this context.
Submitted by: Kazuhiko Uchida [amx02193@mail2.accsnet.ne.jp]
-----------------------------------------------------------------------------
Legionella effectors that promote non-lytic release from protozoa
John Chen1, Karim Suwwan de Felipe 2, Margaret Clarke 3, Hao Lu, 3O.
Roger Anderson4, Gil Segal5 and Howard A. Shuman1
1 Department of Microbiology and 2 Integrated Program in Cellular,
Molecular & Biophysical Studies, College of Physicians & Surgeons,
Columbia University, 701 West 168th Street, New York, NY 10032
3 Program in Molecular and Cell Biology, Oklahoma Medical Research
Foundation, 825 N.E. 13th Street, Oklahoma City, OK 73104-5046
4 Department of Biology, Lamont-Doherty Earth Observatory, Columbia
University, 61 Route 9W, Palisades, NY 10964-1000
5 Department of Molecular Microbiology & Biotechnology, George S. Wise
Faculty of Life Sciences, Tel-Aviv University, Ramat-Aviv, Tel-Aviv 69978,
Israel
Science, in press
Legionella pneumophila, the bacterial agent of legionnairesâ disease,
replicates intracellularly within a specialized vacuole of mammalian and
protozoan host cells. Little is known about the specialized vacuole except
that the Icm/Dot Type IV secretion system is essential for its formation
and maintenance. The Legionella genome database contains two open reading
frames encoding polypeptides (LepA and LepB) with predicted coiled-coil
regions and weak homology to SNAREs; these are delivered to host cells by
an Icm/Dot dependent mechanism. Analysis of mutant strains suggests that
the Lep proteins may enable the Legionella to commandeer a protozoan
exocytic pathway for dissemination of the pathogen.
Submitted by: Margaret Clarke [clarkem@omrf.ouhsc.edu]
-----------------------------------------------------------------------------
Cytosolic [Ca2+]-transients in Dictyostelium discoideum depend on the filling
state of internal stores and on an active SERCA Ca2+-pump
Christina Schlatterer, Kathrin Happle, Daniel F. Lusche and Jrgen Sonnemann+
Faculty for Biology, University of Konstanz, 78457 Konstanz, FRG
+ Institute of Pharmacology, Pediatric Oncology and Hematology, University
of Greifswald, 17487 Greifswald, FRG
J. Biol. Chem., in press
Stimulation of Dictyostelium discoideum with cAMP evokes a change of the
cytosolic free Ca2+ concentration ([Ca2+]i). We analyzed the role of the
filling state of Ca2+-stores for the [Ca2+]i-transient. Parameters tested
were the height of the [Ca2+]i-elevation and the percentage of responding
amoebae. After loading stores with Ca2+, cAMP induced a [Ca2+]i-transient
in many cells. Without prior loading cAMP evoked a [Ca2+]i-change in few
cells only. This indicates that the [Ca2+]i-elevation is not mediated
exclusively by Ca2+-influx but also by Ca2+-release from stores. Reducing
the Ca2+-content of the stores by EGTA-preincubation led to a cAMP-activated
[Ca2+]i-increase even at low extracellular [Ca2+]. Moreover, addition of
Ca2+ itself elicited a capacitative [Ca2+]i-elevation. This effect was not
observed when stores were emptied by the standard technique of inhibiting
internal Ca2+-pumps with 2,5-di-(t-butyl)-1,4-hydroquinone (BHQ). Therefore
in Dictyostelium, an active internal Ca2+-ATPase is absolutely required to
allow for Ca2+-entry. No influence of the filling state of stores on
Ca2+-influx characteristics was found by the Mn2+-quenching technique which
monitors the rate of Ca2+-entry. Both, basal and cAMP-activated Mn2+-influx
rates were similar in control cells and cells with empty stores. By contrast,
determination of extracellular free Ca2+ concentration ([Ca2+]e)-changes
which represent the sum of Ca2+-influx and efflux revealed a higher rate of
[Ca2+]e-decrease in EGTA-treated than in control amoebae. We conclude that
emptying of Ca2+-stores does not change the rate of Ca2+-entry but results
in inhibition of the plasma membrane Ca2+-ATPase. Furthermore, the activities
of the Ca2+-transport ATPases of the stores is of crucial importance for the
regulation of [Ca2+]i-changes.
Submitted by: Christina Schlatterer [Christina.Schlatterer@uni-konstanz.de]
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[End Dicty News, volume 22, number 5]
