dictyNews
Electronic Edition
Volume 39, number 22
August 2, 2013
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Abstracts
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Biological soliton in multicellular movement
Hidekazu Kuwayama, Shuji Ishida
Scientific Reports, 3, Article number: 2272
Solitons have been observed in various physical phenomena. Here,
we show that the distinct characteristics of solitons are present in the
mass cell movement of non-chemotactic mutants of the cellular slime
mould Dictyostelium discoideum. During starvation, D. discoideum
forms multicellular structures that differentiate into spore or stalk cells
and, eventually, a fruiting body. Non-chemotactic mutant cells do not
form multicellular structures; however, they do undergo mass cell
movement in the form of a pulsatile soliton-like structure (SLS). We
also found that SLS induction is mediated by adhesive cell-cell i
nteractions. These observations provide novel insights into the
mechanisms of biological solitons in multicellular movement.
Submitted by Hidekazu Kuwayama [[log in to unmask]]
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A Unique Mitochondrial Transcription Factor B Protein in
Dictyostelium discoideum.
Sam Manna (1), Phuong Le (2), Christian Barth (1)
(1) Department of Microbiology, La Trobe University, Melbourne,
Victoria, Australia,
(2) Tokyo Metropolitan University, Department of Biological Science,
Tokyo, Japan
PLoS ONE 8(7): e70614. doi:10.1371/journal.pone.0070614
Unlike their bacteriophage homologs, mitochondrial RNA polymerases
require the assistance of transcription factors in order to transcribe
mitochondrial DNA efficiently. The transcription factor A family has been
shown to be important for transcription of the human mitochondrial DNA,
with some of its regulatory activity located in its extended C-terminal tail.
The mitochondrial transcription factor B family often has functions not only
in transcription, but also in mitochondrial rRNA modification, a hallmark of
its alpha-proteobacterial origin. We have identified and characterised a
mitochondrial transcription factor B homolog in the soil dwelling cellular
slime mould Dictyostelium discoideum, an organism widely established
as a model for studying eukaryotic cell biology. Using in bacterio functional
assays, we demonstrate that the mitochondrial transcription factor B
homolog not only functions as a mitochondrial transcription factor, but that
it also has a role in rRNA methylation. Additionally, we show that the
transcriptional activation properties of the D. discoideum protein are
located in its extended C-terminal tail, a feature not seen before in the
mitochondrial transcription factor B family, but reminiscent of the human
mitochondrial transcription factor A. This report contributes to our current
understanding of the complexities of mitochondrial transcription, and its
evolution in eukaryotes.
Submitted by Christian Barth [[log in to unmask]]
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Protein phosphatase 4 is involved in the late development of
Dictyostelium discoideum
Ichiro Kamei, Kozo Takamoto, Naoya Sakuragi, Eiji Tanesaka,
Motonobu Yoshida
Open J. Molecu. Integra. Physiol., in press
A cDNA clone SSJ337 (accession no. AF161253) of 1,230 bp,
encoding a catalytic subunit of protein phosphatase 4, was selected as
one of the clones expressed specifically in prestalk cells from a cDNA
library of D. discoideum slugs. Cells transformed with a knockout
construct of SSJ337 showed an aberrant and tiny fruiting-body formation
with a short stalk. A knockout mutant, SSJ337KO was allowed to develop
much slower than a wild-type AX2 after the post-aggregation stage. This
suggested that the SSJ337 cDNA clone played an important role especially
in the late development of Dictyostelium discoideum. Results from
Northern blotting analysis showed that transcripts for SSJ337 were
accumulated at 16 h to 24 h after starvation began.
Submitted by Motonobu Yoshida [[log in to unmask]]
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Social amoeba farmers carry defensive symbionts to protect and privatize
their crops
Debra A. Brock (1), Silven Read (2), Alona Bozhchenko (2), David C.
Queller (1}, and Joan E. Strassmann (1 )
(1) Department of Biology, Washington University at St. Louis, St. Louis,
Missouri 63130, USA
(2) Department of Ecology and Evolutionary Biology, Rice University,
Houston, Texas 77005, USA
Nature Communications, in press
Agricultural crops are investments that can be exploited by others. Farmer
clones of the social amoeba Dictyostelium discoideum carry bacteria to
seed out new food populations but they also carry other non-food bacteria
such as Burkholderia spp. Here we demonstrate that these farmer-carried
Burkholderia inhibit the growth of non-farmer D. discoideum clones that
could exploit the farmer’s crops. Using supernatants, we show that inhibition
is due to molecules secreted by Burkholderia. When farmer and non-farmer
amoebae are mixed together at various frequencies and allowed to complete
the social stage, the ability of non-farmers to produce spores falls rapidly with
an increase in the percentage of farmers with their defensive symbionts, but
conversely, farmer spore production is unaffected by the frequency of farmers.
Our results suggest that successful farming is a complex evolutionary a
daptation, because it requires additional strategies, like recruiting third parties,
to effectively defend and privatize crops.
Submitted by David Queller [[log in to unmask]]
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A bacterial symbiont is converted from an inedible producer of beneficial
molecules into food by a single mutation in the gacA gene
Pierre Stallforth (1), Debra A. Brock (2), Alexandra M. Cantley (1), Xiangjun
Tian (2), David C. Queller (2), Joan E. Strassmann (2), Jon Clardy (1)
(1) Department of Biological Chemistry and Molecular Pharmacology,
Harvard Medical School, Boston, MA 02115
(2) Department of Biology, Washington University in St. Louis,
St. Louis, MO 63130
PNAS , in press; available online
http://www.pnas.org.ezproxy.rice.edu/content/early/2013/07/26/1308199110.abstract
Stable multipartite mutualistic associations require that all partners benefit.
We show that a single mutational step is sufficient to turn a symbiotic bacterium
from an inedible but host-beneficial secondary metabolite producer into a host
food source. The bacteria’s host is a “farmer” clone of the social amoeba
Dictyostelium discoideum that carries and disperses bacteria during its spore
stage. Associated with the farmer are two strains of Pseudomonas fluorescens,
only one of which serves as a food source. The other strain produces diffusible s
mall molecules: pyrrolnitrin, a known antifungal agent, and a chromene that potently
enhances the farmer’s spore production and depresses a nonfarmer’s spore
production. Genome sequence and phylogenetic analyses identify a derived point
mutation in the food strain that generates a premature stop codon in a global
activator (gacA), encoding the response regulator of a two-component regulatory
system. Generation of a knockout mutant of this regulatory gene in the nonfood
bacterial strain altered its secondary metabolite profile to match that of the food
strain, and also, independently, converted it into a food source. These results
suggest that a single mutation in an inedible ancestral strain that served a
protective role converted it to a “domesticated” food source.
Submitted by David Queller [[log in to unmask]]
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Kin Recognition Protects Cooperators Against Cheaters
Hsing-I Ho, Shigenori Hirose, Adam Kuspa, and Gad Shaulsky
Baylor College of Medicine, Houston, TX 77030
Current Biology, in press
The evolution of sociality and altruism is enigmatic because cooperators
are constantly threatened by cheaters who benefit from cooperation without
incurring its full cost. Kin recognition is the ability to recognize and cooperate
with genetically close relatives. It has also been proposed as a potential
mechanism that limits cheating, but there has been no direct experimental
support for that possibility. Here we show that kin recognition protects
cooperators against cheaters. The social amoebae Dictyostelium discoideum
cooperate by forming multicellular aggregates that develop into fruiting bodies
of viable spores and dead stalk cells. Cheaters preferentially differentiate into
spores while their victims die as stalk cells in chimeric aggregates. We
engineered syngeneic cheaters and victims that differed only in their
kin-recognition genes, tgrB1 and tgrC1, and in a single cheater allele and
found that the victims escaped exploitation by different types of nonkin
cheaters. This protection depends on kin-recognition-mediated segregation
because it is compromised when we disrupt strain segregation. These
findings provide direct evidence for the role of kin recognition in cheater
control and suggest a mechanism for the maintenance of stable
cooperative systems.
Submitted by Gad Shaulsky [[log in to unmask]]
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The cytohesin paralog Sec7 of Dictyostelium discoideum is required for
phagocytosis and cell motility
Müller, R., Herr, C., Sukumaran, S. K., Omosigho, N. N., Plomann, M.,
Riyahi, T. Y., Stumpf, M., Swaminathan, K., Tsangarides, M., Yiannakou, K.,
Blau-Wasser, R., Gallinger, C., Schleicher ,M., Kolanus, W., Noegel A. A.
Cell Communication and Signaling , in press
Background: Dictyostelium harbors several paralogous Sec7 genes that
encode members of three subfamilies of the Sec7 superfamily of guanine
nucleotide exchange factors. One of them is the cytohesin family
represented by three members in D. discoideum, SecG, Sec7 and a further
protein distinguished by several transmembrane domains. Cytohesins are
characterized by a Sec7-PH tandem domain and have roles in cell adhesion
and migration.
Results: We study here Sec7. In vitro its PH domain bound preferentially to
phosphatidylinositol 3,4-bisphosphate (PI(3,4)P2), phosphatidylinositol 4,5-
bisphosphate (PI(4,5)P2) and phosphatidylinositol 3,4,5-trisphosphate
(PI(3,4,5)P3). When following the distribution of GFP-Sec7 in vivo we
observed the protein in the cytosol and at the plasma membrane. Strikingly,
when cells formed pseudopods, macropinosomes or phagosomes, GFP-Sec7
was conspicuously absent from areas of the plasma membrane which were
involved in these processes. Mutant cells lacking Sec7 exhibited an impaired
phagocytosis and showed significantly reduced speed and less persistence
during migration. cellular properties associated with mammalian cytohesins
like cell-cell and cell-substratum adhesion were not altered. Proteins with
roles in membrane trafficking and signal transduction have been identified
as putative interaction partners consistent with the data obtained from mutant
analysis.
Conclusions: Sec7 is a cytosolic component and is associated with the
plasma membrane in a pattern distinctly different from the accumulation of
PI(3,4,5)P3. Mutant analysis reveals that loss of the protein affects cellular
processes that involve membrane flow and the actin cytoskeleton.
Submitted by Angelika Noegel [[log in to unmask]]
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[End dictyNews, volume 39, number 21]
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