dictyNews
Electronic Edition
Volume 39, number 18
June 21, 2013

Please submit abstracts of your papers as soon as they have been
accepted for publication by sending them to [log in to unmask]
or by using the form at
http://dictybase.org/db/cgi-bin/dictyBase/abstract_submit.

Back issues of dictyNews, the Dicty Reference database and other
useful information is available at dictyBase - http://dictybase.org.

Follow dictyBase on twitter:
http://twitter.com/dictybase


=========
Abstracts
=========



Lipid composition of multilamellar bodies secreted by Dictyostelium 
discoideum reveals their amoebal origin.

Paquet VE, Lessire R, Domergue F, Fouillen L, Filion G, Sedighi A, 
Charette SJ.

Institut de Biologie Intégrative et des Systèmes, Université Laval, 
Quebec City, Quebec, Canada, G1V 0A6.


Eukaryot Cell. 2013 Jun 7. [Epub ahead of print]

When they are fed with bacteria, Dictyostelium discoideum amoebae 
produce and secrete multilamellar bodies (MLBs), which are composed 
of membranous material. It has been proposed that MLBs are a waste 
disposal system allowing D. discoideum to eliminate undigested 
bacterial remains. However, the real function of MLBs remains unknown. 
Determining the biochemical composition of MLBs, especially lipids, 
represents a way to gain information about the role of these structures. 
To allow these analyses, a protocol involving various centrifugation 
procedures has been developed to purify secreted MLBs from 
amoebae-bacteria co-cultures. The purity of MLB preparation was 
confirmed by transmission electron microscopy and by 
immunofluorescence using H36, an antibody that binds to MLBs. 
The lipid and fatty acid compositions of pure MLBs were then analyzed 
by high performance thin layer chromatography (HPTLC) and gas 
chromatography (GC), respectively, and compared to those of amoebae 
as well as bacteria used as food source. While the bacteria were devoid 
of phosphatidylcholine (PC) and phosphatidylinositol (PI), these two polar 
lipid species were major classes of lipids in MLBs and amoebae. Similarly, 
the fatty acid composition of MLBs and amoebae was characterized by the 
presence of polyunsaturated fatty acids while cyclic fatty acids were found 
only in bacteria. These results strongly suggest that the lipids constituting 
the MLBs rather originate from the amoebal metabolism rather than from 
undigested bacterial membranes. This opens the possibility that MLBs, 
instead of being a waste disposal system, have unsuspected roles in 
D. discoideum physiology.


Submitted by Steve Charette [[log in to unmask]]
---------------------------------------------------------------------------


Laurence Aubry & Gérard Klein

True Arrestins and Arrestin-Fold Proteins: A Structure-Based Appraisal.


Progress in Molecular Biology and Translational Science, Louis M. Luttrell, 
editor, Vol. 118, Burlington: Academic Press, 2013, pp. 21-56.
ISBN: 978-0-12-394440-5

Arrestin-clan proteins are folded alike, a feature responsible for their recent 
grouping in a single clan. In human, it includes the well-characterized visual 
and beta-arrestins, the arrestin domain-containing proteins (ARRDCs), 
isoforms of the retromer subunit VPS26, and DSCR3, a protein involved in 
Down syndrome. A new arrestin-fold-predicted protein, RGP1, described 
here may join the clan. Unicellular organisms like the yeast Saccharomyces 
cerevisiae or the amoeba Dictyostelium discoideum harbor VPS26, DSCR3, 
and RGP1 isoforms as well as arrestin-related trafficking adaptors or ADCs,
 but true arrestins are missing. Functionally, members of the arrestin clan 
 have generally a scaffolding role in various membrane protein trafficking 
 events. Despite their similar structure, the mechanism of cargo recognition 
 and internalization and the nature of recruited partners differ for the different 
 members. Based on the recent literature, true arrestins (visual and 
 beta-arrestins), ARRDCs, and yeast ARTS are the closest from a functional 
 point of view.


Submitted by Laurence Aubry [[log in to unmask]]
---------------------------------------------------------------------------


Analysis of phenotypic evolution in Dictyostelia highlights developmental 
plasticity as a likely consequence of colonial multicellularity

Maria Romeralo1,2,†, Anna Skiba1,†, Alejandro Gonzalez-Voyer3, 
Christina Schilde1, Hajara Lawal1, Sylwia Kedziora1, Jim C. Cavender4, 
Gernot Gloeckner5,6, Hideko Urushihara7 and Pauline Schaap1

1College of Life Sciences, University of Dundee, Dundee, UK
2Department of Systematic Biology, Uppsala University, Uppsala, Sweden
3Department of Integrative Ecology, Estacion Biologica de Donana 
(EBD-CSIC), Sevilla, Spain
4Department of Environmental and Plant Biology, Ohio University, 
Athens, OH, USA
5Department of Genomics, Leibniz-Institute of Freshwater Ecology 
and Inland Fisheries, IGB, Berlin, Germany
6Institute for Biochemistry I, University of Cologne, Cologne, Germany
7Faculty of Life and Environmental Sciences, University of Tsukuba, 
Tsukuba-shi, Japan


Proc. R. Soc. B., in press

Colony formation was the first step towards evolution of multicellularity 
in many macroscopic organisms. Dictyostelid social amoebas have 
used this strategy for over 600 Myr to form fruiting structures of 
increasing complexity. To understand in which order multicellular 
complexity evolved, we measured 24 phenotypic characters over 99 
dictyostelid species. Using phylogenetic comparative methods, we 
show that the last common ancestor (LCA) of Dictyostelia probably 
erected small fruiting structures directly from aggregates. It secreted 
cAMP to coordinate fruiting body morphogenesis, and another 
compound to mediate aggregation. This phenotype persisted up to 
the LCAs of three of the four major groups of Dictyostelia. The 
group 4 LCA co-opted cAMP for aggregation and evolved much 
larger fruiting structures. However, it lost encystation, the survival 
strategy of solitary amoebas that is retained by many species in 
groups 1–3. Large structures, phototropism and a migrating 
intermediate ‘slug’ stage coevolved as evolutionary novelties within 
most groups. Overall, dictyostelids show considerable plasticity in 
the size and shape of multicellular structures, both within and 
between species. This probably reflects constraints placed by colonial 
life on developmental control mechanisms, which, depending on local 
cell density, need to direct from 10 to a million cells into forming a 
functional fructification.


Submitted by Pauline Schaap [[log in to unmask]]
---------------------------------------------------------------------------


Two distinct functions for PI3-kinases in macropinocytosis

Oliver Hoeller, Parvin Bolourani, Jonathan Clark, Len R. Stephens, 
Phillip T. Hawkins, Orion D. Weiner, Gerald Weeks & Robert R. Kay 


Journal of Cell Science, in press

Class-1 PI3-kinases are major regulators of the actin cytoskeleton, 
whose precise contributions to chemotaxis, phagocytosis and 
macropinocytosis remain unresolved. We use systematic genetic 
ablation to examine this question in growing Dictyostelium cells.  
Mass-spectroscopy shows that a quintuple mutant lacking the entire 
genomic complement of class-1 PI3-kinases retains only 10% of 
wild-type PIP3 levels.  Chemotaxis to folate and phagocytosis of 
bacteria proceed normally in the quintuple mutant but 
macropinocytosis is abolished. In this context PI3-kinases show 
specialized functions, only one of which is directly linked to gross 
PIP3 levels: Macropinosomes originate in patches of PIP3, with 
associated F-actin rich ruffles, both of which depend on PI3K1/2 
but not PI3K4, whereas conversion of ruffles into vesicles requires 
PI3K4.  A biosensor derived from the Ras-binding domain of PI3K1 
suggests that Ras is activated throughout vesicle formation.  
Binding assays show that RasG and RasS interact most strongly 
with PI3K1/2 and PI3K4 and single mutants of either Ras have 
severe macropinocytosis defects. Thus, the fundamental function 
of PI3-kinases in growing Dictyostelium cells is in macropinocytosis 
where they have two distinct functions, supported by at least two 
separate Ras proteins.
 
 
Submitted by Oliver Hoeller [[log in to unmask]]
==============================================================
[End dictyNews, volume 39, number 18]