Protist, Vol. 169, 584–602, xx 2018 http://www.elsevier.de/protis Published online date 21 April 2018 ORIGINAL PAPER Calcineurin Silencing in Dictyostelium discoideum Leads to Cellular Alterations Affecting Mitochondria, Gene Expression, and Oxidative Stress Response Konstanze Kobel-Höller a , Kevin Gley a , Janina Jochinke b , Kristina Heider a , Verena Nadin Fritsch a , Ha Viet Duc Nguyen a , Timo Lischke c , Renate Radek b , Ria Baumgrass c,d , Rupert Mutzel a , and Sascha Thewes a,1 a Institute for Biology – Microbiology, Department of Biology, Chemistry, Pharmacy, Freie Universität Berlin, Königin-Luise-Str. 12-16, 14195 Berlin, Germany b Institute for Biology – Zoology, Department of Biology, Chemistry, Pharmacy, Freie Universität Berlin, Königin-Luise-Str. 1-3, 14195 Berlin, Germany c German Rheumatism Research Center (DRFZ), A Leibniz Institute, Charitéplatz 1, 10117 Berlin, Germany d Institute for Biochemistry and Biology, University of Potsdam, Karl-Liebknecht-Str. 24-25, 14476 Potsdam, Germany Submitted July 26, 2017; Accepted April 11, 2018 Monitoring Editor: Chris Howe Calcineurin is involved in development and cell differentiation of the social amoeba Dictyostelium discoideum. However, since knockouts of the calcineurin-encoding genes are not possible in D. dis- coideum it is assumed that the phosphatase also plays a crucial role during vegetative growth of the amoebae. Therefore, we investigated the role of calcineurin during vegetative growth in D. dis- coideum. RNAi-silenced calcineurin mutants showed cellular alterations with an abnormal morphology of mitochondria and had increased content of mitochondrial DNA (mtDNA). In contrast, mitochon- dria showed no substantial functional impairment. Calcineurin-silencing led to altered expression of calcium-regulated genes as well as mitochondrially-encoded genes. Furthermore, genes related to oxidative stress were higher expressed in the mutants, which correlated to an increased resistance towards reactive oxygen species (ROS). Most of the changes observed during vegetative growth were not seen after starvation of the calcineurin mutants. We show that impairment of calcineurin led to many subtle, but in the sum crucial cellular alterations in vegetative D. discoideum cells. As these alterations were not observed after starvation we propose a dual role for calcineurin during growth and develop- ment. Our results imply that calcineurin is one player in the mutual interplay between mitochondria and ROS during vegetative growth. © 2018 Elsevier GmbH. All rights reserved. Key words: mtDNA; mitochondrial remodelling; calcium; oxidative stress; phototaxis. 1 Corresponding author; e-mail sascha.thewes@fu-berlin.de (S. Thewes). https://doi.org/10.1016/j.protis.2018.04.004 1434-4610/© 2018 Elsevier GmbH. All rights reserved.