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dictyNews Volume 33 Number 07
dictyNews
Electronic Edition
Volume 33, number 7
September 11, 2009
Please submit abstracts of your papers as soon as they have been
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Abstracts
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Cheater-resistance is not futile
Anupama Khare, Lorenzo Santorelli, Joan E. Strassmann,
David C. Queller, Adam Kuspa and Gad Shaulsky
Baylor College of Medicine and Rice University
Nature, in press
Cooperative social systems are susceptible to cheating by individuals that
reap the benefits of cooperation without incurring the costs. There are various
theoretical mechanisms for the repression of cheating and many have been
tested experimentally. One possibility that has not been tested rigorously is
the evolution of mutations that confer resistance to cheating. Here we show
that the presence of a cheater in a population of randomly mutated social
amoebae can select for cheater-resistance. Furthermore, we show that this
cheater-resistance can be a noble strategy because the resistor strain does
not necessarily exploit other strains. Thus, the evolution of resistors may be
instrumental in preserving cooperative behavior in the face of cheating.
Submitted by Gad Shaulsky [gadi@bcm.edu]
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P180- mediated trafficking of Vamp7B limits homotypic fusion of Dictyostelium
contractile vacuoles
Yujia Wen, Irene Stavrou, Kirill Bersuker, Rebecca J. Brady, Arturo De Lozanne
and Theresa J. O’Halloran
Molecular, Cell & Dev Biology, University of Texas, Austin
Molecular Biology of the Cell, in press
Clathrin coated vesicles play an established role in endocytosis from the plasma
membrane, but are also found on internal organelles. We examined the composition
of clathrin coated vesicles on an internal organelle responsible for osmoregulation,
the Dictyostelium discoideum contractile vacuole. Clathrin puncta on contractile
vacuoles contained multiple accessory proteins typical of plasma membrane coated
pits, including AP2, AP180, and epsin, but not Hip1r. To examine how these clathrin
accessory proteins influenced the contractile vacuole, we generated cell lines that
carried single and double gene knockouts in the same genetic background. Single
or double mutants that lacked AP180 or AP2 exhibited abnormally large contractile
vacuoles. The enlarged contractile vacuoles in AP180 null mutants formed because
of excessive homotypic fusion among contractile vacuoles. The SNARE protein
Vamp7B, was mislocalized and enriched on the contractile vacuoles of AP180 null
mutants. In vitro assays revealed that AP180 interacted with the cytoplasmic domain
of Vamp7B. We propose that AP180 directs Vamp7B into clathrin coated vesicles
on contractile vacuoles, creating an efficient mechanism for regulating the internal
distribution of fusion-competent SNARE proteins and limiting homotypic fusions
among contractile vacuoles. Dictyostelium contractile vacuoles offer a valuable
system to study clathrin coated vesicles on cell internal organelles.
Submitted by Terry O'Halloran [t.ohalloran@mail.utexas.edu]
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[End dictyNews, volume 33, number 7]
