title: Natural synchronisation for the study of cell division in the green unicellular alga Ostreococcus tauri.
abstract: Ostreococcus tauri (Prasinophyceae) is a marine unicellular green alga which diverged early in the green lineage. The interest of O. tauri as a potential model to study plant cell division is based on its key phylogenetic position, its simple binary division, a very simple cellular organisation and now the availability of the full genome sequence. In addition O. tauri has a minimal yet complete set of cell cycle control genes. Here we show that division can be naturally synchronised by light/dark cycles and that organelles divide before the nucleus. This natural synchronisation, although being only partial, enables the study of the expression of CDKs throughout the cell cycle. The expression patterns of OtCDKA and OtCDKB were determined both at the mRNA and protein levels. The single OtCDKA gene is constantly expressed throughout the cell cycle, whereas OtCDKB is highly regulated and expressed only in S/G2/M phases. More surprisingly, OtCDKA is not phosphorylated at the tyrosine residue, in contrast to OtCDKB which is strongly phosphorylated during cell division. OtCDKA kinase activity appears before the S phase, indicating a possible role of this protein in the G1/S transition. OtCDKB kinase activity occurs later than OtCDKA, and its tyrosine phosphorylation is correlated to G2/M, suggesting a possible control of the mitotic activity. To our knowledge this is the first organism in the green lineage which showed CDKB tyrosine phosphorylation during cell cycle progression.
authors.affiliation: Laboratoire Arago, Observatoire Océanologique, UMR 7628 CNRS - Université ParisVI, BP44 66651, France.
authors.forename: Benoît
authors.initials: B
authors.lastname: Farinas
authors.forename: Camille
authors.initials: C
authors.lastname: Mary
authors.forename: Carmem-Lara
authors.initials: CL
authors.lastname: de O Manes
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Bhaud
authors.forename: Gérard
authors.initials: G
authors.lastname: Peaucellier
authors.forename: Hervé
authors.initials: H
authors.lastname: Moreau
mesh_terms: D001483:Base Sequence; D002455:Cell Division; D000460:Chlorophyta / Q000166:cytology* / Q000201:enzymology / Q000648:ultrastructure; D018844:Cyclin-Dependent Kinases / Q000235:genetics / Q000378:metabolism; D017931:DNA Primers; D005434:Flow Cytometry; D046529:Microscopy, Electron, Transmission; D010766:Phosphorylation; D012333:RNA, Messenger / Q000235:genetics
chemical_list: D017931:DNA Primers; D012333:RNA, Messenger; D018844:Cyclin-Dependent Kinases