The SET Domain Protein, Set3p, Promotes the Reliable Execution of Cytokinesis in Schizosaccharomyces pombe Stefan Rentas1, Reza Saberianfar1, Charnpal Grewal1, Rachelle Kanippayoor1, Mithilesh Mishra2, Dannel McCollum3, Jim Karagiannis1* 1 Department of Biology, University of Western Ontario, London, Ontario, Canada, 2 Temasek Life Sciences Laboratory, The National University of Singapore, Singapore, Singapore, 3 Department of Molecular Genetics and Microbiology, University of Massachusetts Medical School, Worcester, Massachusetts, United States of America Abstract In response to perturbation of the cell division machinery fission yeast cells activate regulatory networks that ensure the faithful completion of cytokinesis. For instance, when cells are treated with drugs that impede constriction of the actomyosin ring (low doses of Latrunculin A, for example) these networks ensure that cytokinesis is complete before progression into the subsequent mitosis. Here, we identify three previously uncharacterized genes, hif2, set3, and snt1, whose deletion results in hyper-sensitivity to LatA treatment and in increased rates of cytokinesis failure. Interestingly, these genes are orthologous to TBL1X, MLL5, and NCOR2, human genes that encode components of a histone deacetylase complex with a known role in cytokinesis. Through co-immunoprecipitation experiments, localization studies, and phenotypic analysis of gene deletion mutants, we provide evidence for an orthologous complex in fission yeast. Furthermore, in light of the putative role of the complex in chromatin modification, together with our results demonstrating an increase in Set3p levels upon Latrunculin A treatment, global gene expression profiles were generated. While this analysis demonstrated that the expression of cytokinesis genes was not significantly affected in set3D backgrounds, it did reveal defects in the ability of the mutant to regulate genes with roles in the cellular response to stress. Taken together, these findings support the existence of a conserved, multi-protein complex with a role in promoting the successful completion of cytokinesis. Citation: Rentas S, Saberianfar R, Grewal C, Kanippayoor R, Mishra M, et al. (2012) The SET Domain Protein, Set3p, Promotes the Reliable Execution of Cytokinesis in Schizosaccharomyces pombe. PLoS ONE 7(2): e31224. doi:10.1371/journal.pone.0031224 Editor: Juan Mata, University of Cambridge, United Kingdom Received December 1, 2011; Accepted January 4, 2012; Published February 8, 2012 Copyright: 2012 Rentas et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This work was supported by the National Sciences and Engineering Research Council of Canada, the University of Western Ontario Academic Development Fund, and the Canada Foundation for Innovation. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: jkaragia@uwo.ca Introduction The successful completion of cytokinesis requires the intricate interplay of gene products ranging from signaling molecules to elements of the cytoskeleton. Taken together these regulatory mechanisms ensure that cytokinesis occurs in a faithful and dependable manner once every cell cycle and over wide-ranging growth conditions. In Schizosaccharomyces pombe, just as in more developmentally complex eukaryotes, cytokinesis is critically dependent on the assembly and constriction of a contractile actomyosin ring [1,2]. The assembly of the ring occurs at the onset of mitosis through the formation of cortical nodes comprised of proteins with roles in nucleating and assembling actin filaments [3]. Once assembled into a contractile ring, the constriction of the filaments is controlled through the action of a regulatory module referred to as the septation initiation network (SIN). The SIN is comprised of a GTPase-regulated signaling cascade that is involved in proper ring assembly, temporal co-ordination of ring constriction, as well as the deposition of the division septum [4,5]. Given the importance of cytokinesis in cellular growth and development, it is not surprising that evidence supporting the existence of a cytokinesis monitoring system has emerged in S. pombe. This monitoring system has the capacity to 1) halt cell cycle progression at G2/M transition, and 2) stabilize the contractile actomyosin ring upon perturbation of the cell division machinery [6,7,8,9,10,11]. Together, these mechanisms ensure that cytoki- nesis is complete before a new cell cycle begins. Important regulators of the cytokinesis monitoring system include the SIN itself, the Cdc14 family phosphatase, Clp1p, the 14-3-3 protein, Rad24p, and the kinase, Lsk1p [8,9,10,12,13,14]. The critical role of these components can be observed experimentally through the treatment of fission yeast cells with low doses of the actin depolymerising drug, Latrunculin A (LatA) [8,10,12,13,14,15]. At the concentrations used (20–50 times less than that needed to completely depolymerize the actin cytoskel- eton) such treatment leads to a Clp1p and Rad24p dependent delay in mitotic entry and the extended activation of the SIN. This leads to a prolonged cytokinesis-competent state that is charac- terized by continuous repair and re-establishment of the actomyosin ring [8,10,11,13]. Abrogation of this system in clp1D or rad24D mutant backgrounds results in cytokinesis failure and the subsequent generation of inviable, multi-nucleate cells [8,10]. In order to identify other genes with roles in promoting the reliable execution of cytokinesis, a library of S. pombe gene deletion mutants was screened for hyper-sensitivity to LatA (M. Mishra and D. McCollum, unpublished). One of the identified genes – defined by the annotated S. pombe ORF, SPCC1235.09 – encoded a WD repeat protein orthologous to human TBL1X, which is known to PLoS ONE | www.plosone.org 1 February 2012 | Volume 7 | Issue 2 | e31224