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dictyNews Volume 26 Number 01
dictyNews
Electronic Edition
Volume 26, number 1
January 06, 2006
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.
Back issues of dictyNews, the Dicty Reference database and other
useful information is available at dictyBase - http://dictybase.org.
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Abstracts
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Developmental Timing in Dictyostelium is Regulated by the Set1 Histone
Methyltransferase
Jonathan R. Chubb, Gareth Bloomfield, Qikai Xu, Markus Kaller, Al Ivens,
Jason Skelton, Bryan M. Turner, Wolfgang Nellen, Gad Shaulsky,
Robert R. Kay, Wendy A. Bickmore and Robert H. Singer
Department of Cell and Developmental Biology, School of Life Sciences,
University of Dundee, Dundee, DD1 5EH
Developmental Biology, in press
Histone modifying enzymes have enormous potential as regulators of the
large-scale changes in gene expression occurring during differentiation.
It is unclear how different combinations of histone modification coordinate
regimes of transcription during development. We show that different
methylation states of lysine 4 of histone H3 (H3K4) mark distinct
developmental phases of the simple eukaryote, Dictyostelium. We demonstrate
that the enzyme responsible for all mono, di and tri-methylation of H3K4 is
the Dictyostelium homolog of the Set1 histone methyltransferase. In the
absence of Set1, cells display unusually rapid development, characterised
by precocious aggregation of amoebae into multicellular aggregates. Early
differentiation markers are abundantly expressed in growing set1 cells,
indicating the differentiation program is ectopically activated during
growth. This phenotype is caused specifically by the loss of Set1 catalytic
activity. Set1 mutants induce premature differentiation in wild-type cells,
indicating Set1 regulates production of an extra-cellular factor required
for the correct perception of growth conditions. Microarray analysis of
the set1 mutants reveals genomic clustering of mis-expressed genes,
suggesting a requirement for Set1 in the regulation of chromatin-mediated
events at gene clusters.
Submitted by: Jonathan Chubb [j.chubb@dundee.ac.uk]
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Differential effects of HP1 isoforms on mitotic chromosome distribution and
growth in Dictyostelium.
Markus Kaller1, Ursula Euteneuer2 and Wolfgang Nellen1*
1 Abt. Genetik, Kassel University, Heinrich-Plett-Str. 40, 34132 Kassel,
Germany
2 Inst. f. Zellbiologie, LMU, Schillerstr. 42, 80336 München, Germany
*corresponding author
Kassel University, FB 18, Abt. Genetik, Heinrich-Plett-Str. 40, 34132 Kassel,
Germany
Tel.: (++49) 561 804 4805
FAX: (++49) 561 804 4800
Eukaryotic Cell, in press
Heterochromatin protein 1 (HP1) is a well characterised heterochromatin
component conserved from fission yeast to humans. We identified three
HP1-like genes (hcpA, hcpB and hcpC) in the Dictyostelium discoideum genome.
Two of these (hcpA and hcpB) are expressed and the proteins colocalized as
GFP-fusion proteins in one major cluster at the nuclear periphery that was
also characterized by histone H3 lysine 9 dimethylation, a histone
modification so far not described for Dictyostelium. The data strongly
suggest that this cluster represents the centromeres. Both single knock-out
strains displayed only subtle phenotypes, suggesting that both isoforms have
largely overlapping functions. In contrast, disruption of both isoforms
appeared to be lethal. Furthermore, overexpression of a C-terminally
truncated form of HcpA resulted in phenotypically distinct growth defects
that were characterised by a strong decrease in cell viability. Although
genetic evidence implies functional redundancy, overexpression of GFP-HcpA,
but not GFP-HcpB, caused growth defects that were accompanied by an increase
in the frequency of atypic anaphase bridges. Our data indicate that
Dictyostelium cells are sensitive to changes in HcpA and HcpB protein levels
and that the two isoforms display in vivo and in vitro different affinities
to each other. Since the RNAi machinery is frequently involved in chromatin
remodelling, we analysed if knock-outs of RNAi components influenced the
localisation of H3K9 dimethylation and HP1 isoforms in Dictyostelium.
Interestingly, heterochromatin organization appeared to be independent of
functional RNAi.
Submitted by: Wolfgang Nellen [nellen@uni-kassel.de]
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[End dictyNews, volume 26, number 1] 
