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dictyNews Volume 20 Number 08
Dicty News
Electronic Edition
Volume 20, number 8
May 02, 2003
Please submit abstracts of your papers as soon as they have been
accepted for publication by sending them to dicty@northwestern.edu.
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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Genetic Interactions of the E3 Ubiquitin Ligase Component FbxA with cAMP
Metabolism and a Histidine Kinase Signaling Pathway During Dictyostelium
discoideum development
Turgay Tekinay, Herbert L. Ennis, Mary Y. Wu, Margaret Nelson1, Richard H.
Kessin*, and David I. Ratner2,*
Accepted: Eukaryotic Cell
Abstract
Dictyostelium amoebae altered in a gene called fbxA, which is thought to
encode a component of an SCF E3 ubiquitin ligase, have defective
regulation of cell-type proportionality. In chimeras with wild-type cells,
the mutant amoebae form mainly spores, leaving the construction of stalks
to wild-type cells. To examine the role of fbxA and regulated proteolysis
we have recovered the promoter of fbxA and shown that it is expressed in a
pattern resembling that of a prestalk-specific gene until late in
development when it is also expressed in developing spore cells. Because
fbxA cells are developmentally deficient in pure culture, we were able to
select suppressor mutations that promote sporulation of the original
mutant. One suppressor mutation resides within the gene regA, which
encodes a cAMP phosphodiesterase linked to an activating response
regulator domain. In another suppressor, there has been a disruption of
dhkA, a gene encoding a two-component histidine kinase known to influence
Dictyostelium development. RegA appears precociously and in greater
amounts in the fbxA mutant but not in an fbxA/dhkA double mutant, where
RegA is restored to wild-type levels. Because the basis of regA
suppression might involve alterations in cAMP levels during development,
the concentration of cAMP was determined in all strains. The level of cAMP
is relatively constant during multi-cellular development in all strains
except the dhkA mutant, in which it is reduced at least 6-fold. The level
of cAMP in the double mutant dhkA/fbxA is relatively normal. The level of
cAMP in the various mutants does not correlate with spore formation, as
would be expected on the basis of our present understanding of the
signaling pathway leading to the induction of spores. Altered amounts of
RegA and cAMP early in the development of the mutants suggest that both
fbxA and dhkA genes act earlier than previously thought.
Submitted by: Turgay Tekinay [tt420@columbia.edu]
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Dictyostelium and Acanthamoeba myosin II assembly domains go to the cleavage
furrow of Dictyostelium myosin II-null cells
Shi Shu*, Xiong Liu* and Edward D. Korn?
Laboratory of Cell Biology, National Heart, Lung, and Blood Institute,
National Institutes of Health, 9000 Rockville Pike, Bethesda, MD 20892, USA
*These authors contributed equally.
?To whom correspondence should be addressed: Building 50, Room 2517,
National Institutes of Health, Bethesda, MD 20892. Tel.: (301) 496-1616.
Fax: (301) 402-1519. E-mail: edk@nih.gov <mailto:edk@nih.gov>
Pro. Natl. Acad. Sci. USA in press
ABSTRACT
How myosin II localizes to the cleavage furrow of dividing cells is largely
unknown. We show here that a 283-residue protein, AD1, corresponding to the
assembly domain in the tail of Dictyostelium myosin II assembles into
bundles of long tubules when expressed in myosin II-null cells and localizes
to the cleavage furrow of dividing cells. AD1 mutants that do not
polymerize in vitro do not go to the cleavage furrow in vivo. An
assembly-competent polypeptide corresponding to the C-terminal 256 residues
of Acanthamoeba myosin II also goes to the cleavage furrow of Dictyostelium
myosin II-null cells. When over-expressed in wild-type cells, AD1
co-localizes with endogenous myosin II (possibly as a co-polymer) in
interphase, motile and dividing cells and under caps of concanavalin A
receptors but has no effect on myosin II-dependent functions. These results
suggest that neither a specific sequence, other than that required for
polymerization, nor interaction with other proteins is required for
localization of myosin II to the cleavage furrow.
Submitted by: Edward Korn [KornE@NHLBI.NIH.GOV]
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The Dictyostelium discoideum prespore specific catalase B functions to control
late development and to protect spore viability
Ma. Xenia U. Garcia+@ Hannah Alexander+, Dana Mahadeo#&, David A. Cotter#, and
Stephen Alexander+*
+Division of Biological Sciences, University of Missouri, 303 Tucker Hall,
Columbia, MO 65211-7400
# Department of Biological Sciences, University of Windsor, Windsor, Ontario,
N9B 3P4 Canada
@ Current address: Department of Molecular Biology and Pharmacology, Washington
University School of Medicine, St. Louis, MO 63110
& Current address: Laboratory of Cellular and Molecular Biology, NCI, NIH,
37 Covet Dr., Bethesda, MD 20892-4255
Accepted: Biochimica Biophysica Acta (BBA) - Molecular Cell Research
Abstract
Changes in the levels of reactive oxygen species (ROS) have been associated
previously with cell differentiation and development in several systems. Thus,
there is interest in studying the developmental regulation of antioxidant
enzymes, whose activities may modulate ROS levels and subsequent oxidant-mediated
signal transduction events in specific tissues. Our recent identification in
Dictyostelium discoideum of the prespore specific catalase B (CatB) enzyme
suggested a) that the CatB enzyme functions to provide protection to the mature
spores, and b) that the CatB enzyme may have a regulatory role in cell
differentiation and morphogenesis. We have now confirmed both these hypotheses.
We specifically disrupted the catB gene by homologous recombination. The
resulting catB null strain displays a 4-hour delay in development at the time of
normal catB gene expression, followed by slow and asynchronous development of
fruiting bodies, taking 10 hours longer than the isogenic parent strain. The
expression of both prestalk and prespore specific genes was altered in the mutant
both temporally and quantitatively, and the resultant mutant spores had increased
sensitivity to H2O2. This study supports the idea that catalase B functions in
the development of D. discoideum by regulating the level of ROS, and adds to the
growing body of evidence for regulatory roles for ROS.
Submitted by: Hannah Alexander [AlexanderH@missouri.edu]
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[End Dicty News, volume 20, number 8]
