dictyNews
Electronic Edition
Volume 35, number 11
October 21, 2010

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Abstracts
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Functional analyses of lissencephaly-related proteins in Dictyostelium  

Irene Meyer, Oliver Kuhnert, Ralph Gräf 


Seminars in Cell and Developmental Biology, in press

Lissencephaly is a severe brain developmental disease in human infants, 
which is usually caused by mutations in either of two genes, LIS1 and 
DCX. These genes encode proteins interacting with both the microtubule 
and actin systems. Here we review the implications of data on 
Dictyostelium LIS1 for the elucidation of LIS1 function in higher cells 
and emphasize the role of LIS1 and nuclear envelope proteins in nuclear 
positioning, which is also important for coordinated cell migration during 
neocortical development. Furthermore, for the first time we characterize 
Dictyostelium DCX, the only bona fide orthologue of human DCX 
outside the animal kingdom. We show that DCX functionally interacts 
with LIS1 and that both proteins have a cytoskeleton-independent 
function in chemotactic signaling during development. Dictyostelium 
LIS1 is also required for proper attachment of the centrosome to the 
nucleus and, thus, nuclear positioning, where the association of these 
two organelles has turned out to be crucial. It involves not only dynein 
and dynein-associated proteins such as LIS1 but also SUN proteins 
of the nuclear envelope. Analyses of Dictyostelium SUN1 mutants 
have underscored the importance of these proteins for the linkage 
of centrosomes and nuclei and for the maintenance of chromatin 
integrity. Taken together, we show that Dictyostelium amoebae, 
which provide a well established model to study the basic aspects 
of chemotaxis, cell migration and development, are well suited for 
the investigation of the molecular and cell biological basis of 
developmental diseases such as lissencephaly. 


Submitted by Ralph Gräf [rgraef@uni-potsdam.de]
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Molecular characterization of the evolution
of phagosomes

Jonathan Boulais, Matthias Trost, Christian Landry, 
Régis Dieckmann, Emmanuel Levy, Thierry Soldati, 
Stephen Michnick, Pierre Thibault, and Michel Desjardins


Molecular Systems Biology 
(http://www.ncbi.nlm.nih.gov/pubmed/20959821)

Amoeba use phagocytosis to internalize bacteria as a source of 
nutrients, whereas multicellular organisms utilize this process as 
a defense mechanism to kill microbes and, in vertebrates, initiate 
a sustained immune response. By using a large-scale approach to 
identify and compare the proteome and phosphoproteome of 
phagosomes isolated from distant organisms, and by comparative 
analysis over 39 taxa, we identified an ‘ancient’ core of phagosomal 
proteins around which the immune functions of this organelle have 
likely organized. Our data indicated that a larger proportion of the 
phagosome proteome, compared with the whole cell proteome, 
has been acquired through gene duplication at a period coinciding 
with the emergence of innate and adaptive immunity. Our study 
also characterized in detail the acquisition of novel proteins and 
the significant remodeling of the phagosome phosphoproteome 
that contributed to modify the core constituents of this organelle in 
evolution. Our work thus provides the first thorough analysis of the 
changes that enabled the transformation of the phagosome from a 
phagotrophic compartment into an organelle fully competent for 
antigen presentation.


Submitted by Thierry Soldati [thierry.soldati@unige.ch]
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[End dictyNews, volume 35, number 11]