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. ============= Abstracts ============= 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] ----------------------------------------------------------------------------- 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] ============================================================================== [End dictyNews, volume 26, number 1]