dictyNews Volume 26 Number 01

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Dicty News

 · 18 Dec 2023

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]