dictyNews Volume 29 Number 07

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dictyNews 
Electronic Edition 
Volume 29, number 7 
Sptember 2, 2007 

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 
========= 

 

The small RNA repertoire of Dictyostelium discoideum and its regulation  
by components of the RNAi pathway 

Andrea Hinas1,5, Johan Reimegård2, E. Gerhart H. Wagner2, Wolfgang Nellen3,  
Victor R. Ambros4, and Fredrik Söderbom1* 

1Department of Molecular Biology, Biomedical Center, Swedish University of  
Agricultural Sciences, Box 590, SE-75124 Uppsala, Sweden 
2Department of Cell and Molecular Biology, Biomedical Center, Uppsala  
University, Box 596, SE-75124 Uppsala, Sweden 
3Department of Genetics, Kassel University, Heinrich Plett Strasse 40,  
34132 Kassel, Germany 
4Department of Genetics, Dartmouth Medical School, Hanover, NH 03755, USA 
5Present address: Department of Molecular and Cellular Biology, Harvard  
University, 16 Divinity Ave, Cambridge, MA 02138, USA 

*corresponding author 

Nucleic acids research, in press 

Small RNAs play crucial roles in regulation of gene expression in many  
eukaryotes. Here, we report the cloning and characterization of 18-26 nt  
RNAs in the social amoeba Dictyostelium discoideum. This survey uncovered  
developmentally regulated microRNA candidates whose biogenesis, at least  
in one case, is dependent on a Dicer homolog, DrnB. Furthermore, we  
identified a large number of 21 nt RNAs originating from the DIRS-1  
retrotransposon, clusters of which have been suggested to constitute  
centromeres. Small RNAs from another retrotransposon, Skipper, were  
significantly up-regulated in strains depleted of the second Dicer-like  
protein, DrnA, and a putative RNA-dependent RNA polymerase, RrpC. In  
contrast, the expression of DIRS-1 small RNAs was not altered in any of  
the analyzed strains. This suggests the presence of multiple RNAi  
pathways in D. discoideum. In addition, we isolated several small RNAs  
with antisense complementarity to mRNAs. Three of these mRNAs are  
developmentally regulated. Interestingly, all three corresponding genes  
express longer antisense RNAs from which the small RNAs may originate.  
In at least one case, the longer antisense RNA is complementary to the  
spliced but not the unspliced pre-mRNA, indicating synthesis by an  
RNA-dependent RNA polymerase. 

 
Submitted by: Fredrik Söderbom [fredde@xray.bmc.uu.se] 
-------------------------------------------------------------------------------- 

 
Arachidonic acid is a chemoattractant for Dictyostelium 
discoideum cells. 

Ralph H. Schaloske, Dagmar Blaesius , Christina Schlatterer and Daniel F.Lusche 

J.Biosci., in press 

Cyclic AMP is the natural chemoattractant of the social amoebae Dictyostelium  
discoideum. It is detected by cell surface cAMP-receptors. Besides a signalling  
cascade involving phosphatidylinositol 3,4,5-trisphosphate (PIP3),  
Ca2+ signalling has been shown to have a major role in chemotaxis. Previously,  
we have shown that arachidonic acid (AA) induces an increase in the cytosolic  
Ca2+ concentration by releasing Ca2+ from intracellular stores and activating  
influx of extracellular Ca2+. Here we report that AA is a chemoattractant for  
D. discoideum cells differentiated for 8 to 9 hours. Motility towards a glass  
capillary filled with an AA solution was dose-dependent and qualitatively  
comparable to cAMP-induced chemotaxis. Ca2+ played an important role in  
AA chemotaxis of wild type Ax2 as  
ethyleneglycol-bis(b-aminoethyl)-N,N,N’,N’-tetraacetic acid (EGTA) added to  
the extracellular buffer strongly inhibited motility. In the HM1049 mutant  
whose iplA gene encoding a putative Ins(1,4,5)P3-receptor had been knocked  
out,chemotaxis was only slightly affected by EGTA. Chemotaxis in the presence  
of extracellular Ca2+ was similar in both strains. Unlike cAMP, addition of  
AA to a cell suspension did not change cAMP or cGMP levels. A model for  
AA chemotaxis based on the findings in this and previous work is presented. 

 
Submitted by: Daniel F.Lusche [daniel.lusche@web.de] 
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[End dictyNews, volume 29, number 7]