dictyNews
Electronic Edition
Volume 33, number 1
July 3, 2009

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Abstracts
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Histone deacetylases regulate multicellular development in the social
amoeba Dictyostelium discoideum.

Ritwick Sawarkar, Sandhya S Visweswariah, Wolfgang Nellen and
Vidyanand Nanjundiah


Journal of Molecular Biology, in press

Histone modification is believed to be important for the coordinated
regulation of developmental pathways. We have studied the roles of  
histone
deacetylases (HDACs) in the life cycle of Dictyostelium discoideum  
(Ax2).
Our findings are as follows. (1) Bioinformatic analysis shows that there
are four putative HDACs in D. discoideum, two each of class I and  
class II
HDACs. A sequence dendrogram of HDAC domains suggests that the two
classII HDACs (HdaC and HdaD) belong to a subgroup of TSA-insensitive
HDACs along with Hos3 of Saccharomyces cerevisiae. (2) One of the four
HDAC-encoding genes, hdaA, could not be knocked out, probably because
the gene is essential for growth. However, a strain lacking hdaB could  
be
obtained. hdaB is dispensable for growth and development under  
laboratory
conditions but is required in a social context: cells that lack hdaB  
function
develop normally but sporulate less efficiently than the wild type in  
chimeras.
(3) Vegetative cells exhibit HDAC activity in both the nucleus and  
cytosol.
Nuclear activity is completely inhibited by trichostatin A (TSA), a  
specific
inhibitor of non-sirtuin HDACs. On the other hand, cytosolic activity is
resistant to TSA. This suggests that the TSA-insensitive class II HDACs
function in the cytosol whereas the class I enzymes are primarily  
found in
the nucleus. (4) Incubation of growing cells with up to 1 micromolar TSA
causes a moderate increase in histone acetylation without any effect on
generation time. (5) When starving cells are treated with 500 nanomolar
TSA, there is a significant increase in histone acetylation and a  
delay of
about 3-4 hours in development till the mound stage. Differentiation  
too is
delayed in TSA-treated cells but cell type proportions are normal.
(6) TSA-treated cells show robust cyclic AMP oscillations comparable to
control cells but the temporal expression profile of some  
‘developmental’
genes is affected. In particular, a subset of genes regulated by cAMP  
and
protein kinase A is delayed. These are the genes encoding the cell
adhesion molecule contact site A (csaA), and calcium binding proteins
(cbpF and cbpA).

We infer that HDAC activity influences heterochrony, the relative timing
of developmental events, as well as aspects of the phenotype that  
mediate
social behaviour in genetically heterogeneous groups.


Submitted by: Vidyanand Nanjundiah [[log in to unmask]]
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Nanovesicles released by Dictyostelium cells : A potential carrier for
drug delivery

Françoise Laviallea, Sophie Deshayesa, Florence Gonnetb, Eric Larquetc,
Sergei G. Kruglika, Nicolas Boissetc§, Régis Danielb, Annette Alfsend,
Irène Tatischeff a*

a CNRS, UMR7033, Université Pierre et Marie Curie, Laboratoire de  
Biophysique
Moléculaire Cellulaire et Tissulaire, Genopole, F-91030 Evry, France
b CNRS, UMR8587, Université Evry val d’Essonne, Laboratoire Analyse et
Modélisation pour la Biologie et l’Environnement, F-91025 Evry, France
c CNRS, UMR7590, Institut de Minéralogie et de Physique des Milieux
Condensés, Université Pierre et Marie Curie, F-75252 Paris, France
d CNRS, UMR8104, INSERM, U567, Institut Cochin, Département de Biologie
Cellulaire, Université Paris-Descartes, F-75014 Paris, France
§ Nicolas Boisset deceased on January 2008.

*Corresponding author


International Journal of Pharmaceutics, in press

Nanovesicles released by Dictyostelium discoideum cells grown in the
presence of the DNA-specific dye Hoechst 33342 have been previously
shown to mediate the transfer of the dye into the nuclei of Hoechst- 
resistant
cells. The present investigation extends this work by conducting  
experiments
in the presence of hypericin,a fluorescent therapeutic photosensitizer  
assayed
for antitumoral photodynamic therapy. Nanovesicles released by  
Dictyostelium
cells exhibit an averaged diameter between 50 and 150 nm, as measured by
transmission cryoelectron microscopy. A proteomic analysis reveals a
predominance of actin and actin-related proteins. The detection of a
lysosomal membrane protein (LIMP II) indicates that these vesicles are
likely generated in the late endosomal compartment. The use of the  
hypericin-
containing nanovesicles as nanodevices for in vitro drug delivery was
investigated by fluorescence microscopy. The observed signal was almost
exclusively located in the perinuclear area of two human cell lines,  
skin
fibroblasts (HS68) and cervix carcinoma (HeLa) cells. Studies by  
confocal
microscopy with specific markers of cell organelles, provided evidence  
that
hypericin was accumulated in the Golgi apparatus. All these data shed  
a new
light on in vitro drug delivery by using cell-released vesicles as  
carriers.


Submitted by: Irene Tatischeff [ [log in to unmask]]

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[End dictyNews, volume 32, number 1]