title: p53-independent checkpoint controls in a plant cell model.
abstract: Allium cepa L. meristems were used as a plant model to study the p53-independent control of S and G2 phases by checkpoint pathways, in eukaryotic cells. Checkpoint blocks were induced at early and mid S by hydroxyurea. After their spontaneous override, cells became accumulated in G2-prophase, giving rise later on to a delayed mitotic wave. Cell growth was maintained during the checkpoint blocks, as the delayed mitoses were larger in size than the control ones. Under continuous hydroxyurea treatment, the delayed mitotic was formed by two subpopulations: normal mitoses corresponding to cells having properly recovered from the checkpoint block, and abnormal ones resulting from checkpoint adaptation. These latter cells displayed broken chromatids as they had unduly overriden the G2 checkpoint block, without completing DNA repair. The frequency of the checkpoint-adapted mitoses increased with the hydroxyurea concentration from 0.25 to 1.0 mM. However, from 1 mM hydroxyurea upwards, some of the cells lost their competence for checkpoint adaptation. Therefore, the dose of a genotoxic agent that still allows G2 checkpoint adaptation should always be applied in order to get rid of uncontrolled proliferating cells. This is specially suitable for cells lacking a functional p53 protein.
authors: Centro de Investigaciones Biológicas, CSIC, Ramiro de Maeztu, 9. E-28040-Madrid, Spain.
authors: Helvia R
authors: HR
authors: Pelayo
authors: Juana
authors: J
authors: Pincheira
authors: Juan F
authors: JF
authors: Giménez-Abián
authors: Duncan J
authors: DJ
authors: Clarke
authors: Consuelo
authors: C
authors: de la Torre
mesh_terms: D002453:Cell Cycle / Q000187:drug effects; D004260:DNA Repair; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D016195:G2 Phase / Q000187:drug effects / Q000235:genetics; D018816:Genes, cdc / Q000187:drug effects; D006918:Hydroxyurea / Q000494:pharmacology*; D018519:Meristem / Q000166:cytology / Q000187:drug effects*; D008938:Mitosis; D019697:Onions / Q000187:drug effects* / Q000254:growth & development; D016196:S Phase / Q000187:drug effects / Q000235:genetics; D016159:Tumor Suppressor Protein p53 / Q000502:physiology*
chemical_list: D004791:Enzyme Inhibitors; D016159:Tumor Suppressor Protein p53; D006918:Hydroxyurea