dictyNews

Electronic Edition

Volume 47, number 3

January 29, 2021



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Abstracts

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Richa Karmakar, Man-Ho Tang, Haicen Yue, Daniel Lombardo, Aravind 

Karanam, Brian A. Camley, Alex Groisman, and Wouter-Jan Rappel



Cellular memory in eukaryotic chemotaxis depends on the background 

chemoattractant concentration





Phys. Rev. E, 103, 012402 (2021) 



Cells of the social amoeba Dictyostelium discoideum migrate to a 

source of periodic traveling waves of chemoattractant as part of 

a self-organized aggregation process. An important part of this 

process is cellular memory, which enables cells to respond to the 

front of the wave and ignore the downward gradient in the back of 

the wave. During this aggregation, the background concentration 

of the chemoattractant gradually rises. In our microfluidic 

experiments, we exogenously applied periodic waves of 

chemoattractant with various background levels. We find that 

increasing background does not make detection of the wave more 

difficult, as would be naively expected. Instead, we see that the 

chemotactic efficiency significantly increases for intermediate 

values of the background concentration but decreases to almost 

zero for large values in a switch-like manner. These results are 

consistent with a computational model that contains a bistable 

memory module, along with a nonadaptive component. Within this 

model, an intermediate background level helps preserve directed 

migration by keeping the memory activated, but when the background 

level is higher, the directional stimulus from the wave is no 

longer sufficient to activate the bistable memory, suppressing 

directed migration. These results suggest that raising levels of 

chemoattractant background may facilitate the self-organized 

aggregation in Dictyostelium colonies.





submitted by: Wouter-Jan Rappel [[log in to unmask]]

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Abundantly expressed class of non-coding RNAs conserved through 

the multicellular evolution of dictyostelid social amoebae.



Jonas Kjellin1, Lotta Avesson2,3, Johan Reimegård4, Zhen Liao1,5, 

Ludwig Eichinger6, Angelika Noegel6, Gernot Glöckner6,†, 

Pauline Schaap7, and Fredrik Söderbom1



1Department of Cell and Molecular Biology, Uppsala University, 

Box 596 Uppsala, S-75124 Sweden, 

2Department of Molecular Biology, Biomedical Center, Swedish 

University of Agricultural Sciences, Box 590, S-75124 Uppsala, 

Sweden, 

4Department of Cell and Molecular Biology, National Bioinformatics 

Infrastructure Sweden, Science for Life Laboratory, Uppsala 

University, Box 596 Uppsala, S-75124 Sweden, 

6Centre for Biochemistry, Institute of Biochemistry I, Medical 

Faculty, University of Cologne, Cologne, Germany and 

7College of Life Sciences, University of Dundee, Dundee DD1 5EH, 

United Kingdom. 

3Present address: Novo Nordisk Foundation Center for Protein 

Research, University of Copenhagen, Blegdamsvej 3B, 2200 Copenhagen. 

5Present address:  Department of Plant Biology, Swedish University 

of Agricultural Sciences, Box 7080 Uppsala, S-750 07 Sweden, 

† Deceased





Genome Research, in press



Aggregative multicellularity has evolved multiple times in diverse 

groups of eukaryotes, exemplified by the well-studied development 

of dictyostelid social amoebae, e.g. Dictyostelium discoideum. 

However, it is still poorly understood why multicellularity emerged 

in these amoebae while the great majority of other members of 

Amoebozoa are unicellular. Previously a novel type of non-coding 

RNA, Class I RNAs, was identified in D. discoideum and demonstrated 

to be important for normal multicellular development. Here we 

investigated Class I RNA evolution and its connection to 

multicellular development. We identified a large number of new 

Class I RNA genes by constructing a co-variance model combined with 

a scoring system based on conserved up-stream sequences. Multiple 

genes were predicted in representatives of each major group of 

Dictyostelia and expression analysis confirmed that our search 

approach identifies expressed Class I RNA genes with high accuracy 

and sensitivity and that the RNAs are developmentally regulated. 

Further studies showed that Class I RNAs are ubiquitous in 

Dictyostelia and share highly conserved structure and sequence 

motifs. In addition, Class I RNA genes appear to be unique to 

dictyostelid social amoebae since they could not be identified in 

outgroup genomes, including their closest known relatives. Our 

results show that Class I RNA is an ancient class of ncRNAs, likely 

to have been present in the last common ancestor of Dictyostelia 

dating back at least 600 million years. Based on previous 

functional analyses and the presented evolutionary investigation, 

we hypothesize that Class I RNAs were involved in evolution of 

multicellularity in Dictyostelia.





submitted by: Fredrik Söderbom[[log in to unmask]]

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[End dictyNews, volume 47, number 3]