title: Septin filaments exhibit a dynamic, paired organization that is conserved from yeast to mammals.
abstract: The septins are conserved, GTP-binding proteins important for cytokinesis, membrane compartmentalization, and exocytosis. However, it is unknown how septins are arranged within higher-order structures in cells. To determine the organization of septins in live cells, we developed a polarized fluorescence microscopy system to monitor the orientation of GFP dipole moments with high spatial and temporal resolution. When GFP was fused to septins, the arrangement of GFP dipoles reflected the underlying septin organization. We demonstrated in a filamentous fungus, a budding yeast, and a mammalian epithelial cell line that septin proteins were organized in an identical highly ordered fashion. Fluorescence anisotropy measurements indicated that septin filaments organized into pairs within live cells, just as has been observed in vitro. Additional support for the formation of pairs came from the observation of paired filaments at the cortex of cells using electron microscopy. Furthermore, we found that highly ordered septin structures exchanged subunits and rapidly rearranged. We conclude that septins assemble into dynamic, paired filaments in vivo and that this organization is conserved from yeast to mammals.
authors.affiliation: Department of Biological Sciences and 2 EM Facility, Dartmouth College, Hanover, NH 03755, USA.
authors.forename: Bradley S
authors.initials: BS
authors.lastname: DeMay
authors.forename: Xiaobo
authors.initials: X
authors.lastname: Bai
authors.forename: Louisa
authors.initials: L
authors.lastname: Howard
authors.forename: Patricia
authors.initials: P
authors.lastname: Occhipinti
authors.forename: Rebecca A
authors.initials: RA
authors.lastname: Meseroll
authors.forename: Elias T
authors.initials: ET
authors.lastname: Spiliotis
authors.forename: Rudolf
authors.initials: R
authors.lastname: Oldenbourg
authors.forename: Amy S
authors.initials: AS
authors.lastname: Gladfelter
mesh_terms: D000818:Animals; D002460:Cell Line; D003599:Cytoskeleton / Q000378:metabolism / Q000648:ultrastructure*; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008856:Microscopy, Fluorescence / Q000295:instrumentation / Q000379:methods; D008859:Microscopy, Polarization / Q000295:instrumentation / Q000379:methods; D055503:Protein Multimerization; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D058112:Septins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure*; D015003:Yeasts / Q000737:chemistry / Q000166:cytology / Q000378:metabolism
chemical_list: D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D058112:Septins