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dictyNews Volume 38 Number 01
dictyNews
Electronic Edition
Volume 38, number 1
January 6, 2012
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.
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HAPPY 2012!
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Abstracts
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Bimodal distribution of motility and cell fate in Dictyostelium discoideum
Pavana Goury Sistla1, Vidyanand Nanjundiah2, Gopal Pande1
1 Centre for Cellular and Molecular Biology, Uppal Road
Hyderabad 500 007, India
2 Developmental Biology and Genetics Laboratory, Indian Institute
of Science, Bangalore, 560012, India
International Journal of Developmental Biology, in press
Several differences between presumptive spore and presumptive stalk
cells have been reported during the development of Dictyostelium
discoideum from unicellular amoebae into multi-cellular fruiting bodies.
In this paper we have examined whether cell motility-related properties
are also among them. Cell speeds and localisation of motility-related
signalling molecules in single cells were monitored by live cell imaging
and immunostaining under three conditions: (a) in nutrient medium
during growth, (b) immediately following transfer to starvation medium
and (c) in nutrient medium that was re-introduced after a brief period
of starvation. Cells moved randomly under all three conditions but the
mean speed increased following transfer from nutrient medium to
starvation medium. Further, the distribution of speeds in starvation
medium was bimodal: about 20% of the cells moved significantly faster
('fast cells') than the remaining 80% ('slow cells'). Both changes
occurred rapidly, i.e. by 15min of transfer to starvation medium; they
reverted within 15min after restoration of the nutrient medium. The
distribution and organization of the cell motility-related molecules
F-actin, PTEN and PI3 kinase was different in slow and fast cells. Our
data indicate that fast cells were capable of making more pseudopods
and could readily redistribute their cytoskeletal apparatus and
associated molecules, leading to a higher speed. Among starved cells,
the calcium content of slow cells was significantly lower than that of
fast cells. The slow/fast distinction was absent in Polysphondylium
pallidum, a cellular slime mould that lacks the presumptive stalk and
spore cell classes, and also in trishanku (triA-), a mutant of
D. discoideum in which the prestalk and prespore states are unstable.
We infer that very soon after the transition from growth to starvation,
a switch is triggered in some D. discoideum cells, that separates them
into two functional classes: (a) cells that continue to move at (slow)
speeds that are seen in nutrient containing conditions, and whose
calcium content remains at relatively low levels; and (b) cells that move
significantly faster than pre-starvation cells and whose calcium levels
are relatively higher. This switch may be the earliest step in the
generation of the prespore and prestalk cell categories. The existence
of the switch is in accordance with a previously postulated bistable
mechanism underlying cell motility.
Submitted by Pavana Goury Sistla [pavanags@ccmb.res.in]
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Cell-derived microvesicles and antitumoral multidrug resistance
Irene Tatischeff
Laboratoire Acides Nucleiques et Biophotonique (ANBioPhi),
UPMC/CNRS, 4 Place Jussieu, Case Courrier 138, F-75252
Paris Cedex 05, France
Comptes rendus Biologies, in press.
Antitumoral chemotherapeutic treatments are often impaired by
innate or acquired multidrug resistance (MDR). After four decades
of MDR research, having underlined its complexity, new knowledge
about the mechanisms of tumor resistance to antineoplastic drugs
is a prerequisite for improving chemotherapy. Following our
observations with a non-pathogenic eukaryotic microorganism,
Dictyostelium discoideum, I suggest that MDR in tumor cells might
be the consequence of a detoxification mechanism, mediated by
cell-derived microvesicles. Recently published observations with
tumoral human cells support this hypothesis. First, these cell-derived
vesicles might impair chemotherapeutic efficiency of many
structurally-different antineoplastic agents by preventing them to
reach their intracellular target, followed by their expulsion outside
the tumor cells, as observed for Dictyostelium cells. Secondly,
beside their newly recognized function of intercellular communication,
the cell-derived vesicles might also act as intercellular transporters
of multidrug resistance proteins. Experiments are suggested for
checking the hypothesis of cell-derived vesicles mediating multidrug
resistance.
Submitted by Irene Tatischeff [irene.tatischeff@upmc.fr]
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A Gbg Effector, ElmoE, Transduces GPCR Signaling
to the Actin Network during Chemotaxis
Jianshe Yan,1 Vassil Mihaylov,3 Xuehua Xu,1 Joseph A. Brzostowski,
2 Hongyan Li,1 Lunhua Liu,3 Timothy D. Veenstra,4 Carole A. Parent,
3 and Tian Jin1,*
Developmental Cell (2012), doi:10.1016/j.devcel.2011.11.007
Activation of G protein-coupled receptors (GPCRs) leads to the
dissociation of heterotrimeric G-proteins into Ga and Gbg subunits,
which go on to regulate various effectors involved in a panoply of
cellular responses. During chemotaxis, Gbg subunits regulate actin
assembly and migration, but the protein(s) linking Gbg to the actin
cytoskeleton remains unknown. Here, we identified a Gbg effector,
ElmoE in Dictyostelium, and demonstrated that it is required for
GPCR-mediated chemotaxis. Remarkably, ElmoE associates with
Gbg and Dock-like proteins to activate the small GTPase Rac, in a
GPCR-dependent manner, and also associates with Arp2/3 complex
and F-actin. Thus, ElmoE serves as a link between chemoattractant
GPCRs, G-proteins and the actincytoskeleton. The pathway, consisting
of GPCR, Gbg, Elmo/Dock, Rac, and Arp2/3, spatially guides the
growth of dendritic actin networks in pseudopods of eukaryotic cells
during chemotaxis.
Submitted by Jianshe Yan [yanjia@niaid.nih.gov]
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[End dictyNews, volume 38, number 1]
