title: Motor Activity Dependent and Independent Functions of Myosin II Contribute to Actomyosin Ring Assembly and Contraction in Schizosaccharomyces pombe.
abstract: Cytokinesis depends on a contractile actomyosin ring in many eukaryotes [1-3]. Myosin II is a key component of the actomyosin ring, although whether it functions as a motor or as an actin cross-linker to exert its essential role is disputed [1, 4, 5]. In Schizosaccharomyces pombe, the myo2-E1 mutation affects the upper 50 kDa sub-domain of the myosin II heavy chain, and cells carrying this lethal mutation are defective in actomyosin ring assembly at the non-permissive temperature [6, 7]. myo2-E1 also affects actomyosin ring contraction when rings isolated from permissive temperature-grown cells are incubated with ATP [8]. Here we report isolation of a compensatory suppressor mutation in the lower 50 kDa sub-domain (myo2-E1-Sup1) that reverses the inability of myo2-E1 to form colonies at the restrictive temperature. myo2-E1-Sup1 is capable of assembling normal actomyosin rings, although rings isolated from myo2-E1-Sup1 are defective in ATP-dependent contraction in vitro. Furthermore, the product of myo2-E1-Sup1 does not translocate actin filaments in motility assays in vitro. Superimposition of myo2-E1 and myo2-E1-Sup1 on available rigor and blebbistatin-bound myosin II structures suggests that myo2-E1-Sup1 may represent a novel actin translocation-defective allele. Actomyosin ring contraction and viability of myo2-E1-Sup1 cells depend on the late cytokinetic S. pombe myosin II isoform, Myp2p, a non-essential protein that is normally dispensable for actomyosin ring assembly and contraction. Our work reveals that Myo2p may function in two different and essential modes during cytokinesis: a motor activity-independent form that can promote actomyosin ring assembly and a motor activity-dependent form that supports ring contraction.
authors.affiliation: Division of Biomedical Sciences, Warwick Medical School, University of Warwick, Coventry CV4 7AL, UK. Electronic address: s.palani@warwick.ac.uk.
authors.forename: Saravanan
authors.initials: S
authors.lastname: Palani
authors.affiliation: Division of Biomedical Sciences, Warwick Medical School, University of Warwick, Coventry CV4 7AL, UK.
authors.forename: Ting Gang
authors.initials: TG
authors.lastname: Chew
authors.affiliation: School of Biological Sciences, National Institute of Science Education and Research (NISER), Odisha 752050, India.
authors.forename: Srinivasan
authors.initials: S
authors.lastname: Ramanujam
authors.affiliation: Division of Biomedical Sciences, Warwick Medical School, University of Warwick, Coventry CV4 7AL, UK.
authors.forename: Anton
authors.initials: A
authors.lastname: Kamnev
authors.affiliation: Biology Division, Indian Institute of Science Education and Research (IISER), Pune, Maharashtra 411008, India.
authors.forename: Shrikant
authors.initials: S
authors.lastname: Harne
authors.affiliation: Division of Biomedical Sciences, Warwick Medical School, University of Warwick, Coventry CV4 7AL, UK.
authors.forename: Bernardo
authors.initials: B
authors.lastname: Chapa-Y-Lazo
authors.affiliation: Division of Biomedical Sciences, Warwick Medical School, University of Warwick, Coventry CV4 7AL, UK.
authors.forename: Rebecca
authors.initials: R
authors.lastname: Hogg
authors.affiliation: Temasek Life Sciences Laboratory, 1. Research Link, National University of Singapore, Singapore 117604, Singapore.
authors.forename: Mayalagu
authors.initials: M
authors.lastname: Sevugan
authors.affiliation: Temasek Life Sciences Laboratory, 1. Research Link, National University of Singapore, Singapore 117604, Singapore; Department of Biological Sciences, Tata Institute of Fundamental Research (TIFR), Mumbai, Maharashtra 400005, India.
authors.forename: Mithilesh
authors.initials: M
authors.lastname: Mishra
authors.affiliation: Biology Division, Indian Institute of Science Education and Research (IISER), Pune, Maharashtra 411008, India.
authors.forename: Pananghat
authors.initials: P
authors.lastname: Gayathri
authors.affiliation: Division of Biomedical Sciences, Warwick Medical School, University of Warwick, Coventry CV4 7AL, UK. Electronic address: m.k.balasubramanian@warwick.ac.uk.
authors.forename: Mohan K
authors.initials: MK
authors.lastname: Balasubramanian
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism; D000205:Actomyosin / Q000502:physiology; D048749:Cytokinesis; D024462:Myosin Type II / Q000502:physiology*; D012568:Schizosaccharomyces / Q000502:physiology*; D029702:Schizosaccharomyces pombe Proteins / Q000502:physiology*
chemical_list: D029702:Schizosaccharomyces pombe Proteins; D000205:Actomyosin; D024462:Myosin Type II
keywords: S. pombe; actin; actomyosin ring; cytokinesis; myosin-II