title: Evolution of zygomycetous spindle pole bodies: Evidence from Coemansia reversa mitosis.
abstract: OBJECTIVE
  The earliest eukaryotes were likely flagellates with a centriole that nucleates the centrosome, the microtubule-organizing center (MTOC) for nuclear division. The MTOC in higher fungi, which lack flagella, is the spindle pole body (SPB). Can we detect stages in centrosome evolution leading to the diversity of SPB forms observed in terrestrial fungi? Zygomycetous fungi, which consist of saprobes, symbionts, and parasites of animals and plants, are critical in answering the question, but nuclear division has been studied in only two of six clades.
  
  
  METHODS
  Ultrastructure of mitosis was studied in Coemansia reversa (Kickxellomycotina) germlings using cryofixation or chemical fixation. Character evolution was assessed by parsimony analysis, using a phylogenetic tree assembled from multigene analyses.
  
  
  RESULTS
  At interphase the SPB consisted of two components: a cytoplasmic, electron-dense sphere containing a cylindrical structure with microtubules oriented nearly perpendicular to the nucleus and an intranuclear component appressed to the nuclear envelope. Markham's rotation was used to reinforce the image of the cylindrical structure and determine the probable number of microtubules as nine. The SPB duplicated early in mitosis and separated on the intact nuclear envelope. Nuclear division appears to be intranuclear with spindle and kinetochore microtubules interspersed with condensed chromatin.
  
  
  CONCLUSIONS
  This is the sixth type of zygomycetous SPB, and the third type that suggests a modified centriolar component. Coemansia reversa retains SPB character states from an ancestral centriole intermediate between those of fungi with motile cells and other zygomycetous fungi and Dikarya.
authors.affiliation: Department of Plant Biology, University of Minnesota, St. Paul, Minnesota 55108-1095 USA.
authors.forename: David J
authors.initials: DJ
authors.lastname: McLaughlin
authors.affiliation: Department of Plant Biology, University of Minnesota, St. Paul, Minnesota 55108-1095 USA.
authors.forename: Rosanne A
authors.initials: RA
authors.lastname: Healy
authors.affiliation: University Imaging Centers, University of Minnesota, St. Paul, Minnesota 55108-1095 USA.
authors.forename: Gail J
authors.initials: GJ
authors.lastname: Celio
authors.affiliation: School of Life Sciences, Arizona State University, Tempe, Arizona 85287 USA.
authors.forename: Robert W
authors.initials: RW
authors.lastname: Roberson
authors.affiliation: Department of Botany, The Zamorin's Guruvayurappan College, Calicut, Kerala 673014 India.
authors.forename: T K Arun
authors.initials: TK
authors.lastname: Kumar
mesh_terms: D019143:Evolution, Molecular; D005658:Fungi / Q000502:physiology* / Q000648:ultrastructure; D008854:Microscopy, Electron; D008938:Mitosis; D009685:Nuclear Envelope / Q000502:physiology / Q000648:ultrastructure; D010802:Phylogeny; D064048:Spindle Pole Bodies / Q000502:physiology* / Q000648:ultrastructure
keywords: centriole; centrosome; fungi; nuclear division; spindle pole body; ultrastructure; zygomycetes