Projet ANR-07-BLAN-0059 – MyGreatOocyte : Coordinating cell division and DNA replication: interplay between Cdc2, Myt1 and a new player, Greatwall
Programme : Blanc (BLANC) 2007
Année de financement : 2007
Coordinateur du projet : Catherine JESSUS (CNRS DELEGATION REGIONALE PARIS B)
Partenaires : Centre national de la recherche scientifique
Montant : 350000.0 euros
Date de début : 2007
Durée : 36 mois
Résumé : "Our project aims for understanding the control of two crucial periods of the cell cycle, M- and S-phases. This project is based on a physiological model system, the meiotic divisions of Xenopus oocyte, broadly used to study cell division. The first objective is to unravel the molecular mechanisms that control the activation of MPF (M-phase Promoting Factor or cyclin B-Cdc2 complex), the universal inducer of the M-phase in eukaryotes. The second objective aims for understanding the mechanisms that repress DNA replication after meiosis I, an essential event to produce a haploid genome. The fundamental knowledge of these crucial periods of the cell cycle is a mandatory step to understand cancer disorders generated by M- and S-phases miss-regulations and the connections between oncogenes, DNA replication and mitosis. -  Great insights in the understanding of cell division came from the discovery of MPF in 1971 and then in the 90s from the molecular identification of this factor and its direct regulators, Cdc25 and Wee1/Myt1. It is now established that the irreversible commitment into M-phase depends on the sudden activation of the Cdc2 kinase promoting, by the phosphorylation of many substrates, major changes of cell architecture required for divisions. MPF activity depends on Cdc2 phosphorylation levels, hence on the balance between its two regulators, the activator phosphatase Cdc25 and the inhibitor kinase Myt1/Wee1. MPF activation is remarkably rapid and total as it follows an ""all-or-nothing"" rule. This is the result of a feedback loop exerted by Cdc2 on its regulators: the more active Cdc2 molecules are, the more they activate Cdc25 and inhibit Wee1/Myt1 and the more rapidly Cdc2 activates. However, the molecular mechanisms generating the very first active MPF molecules to start the auto-amplification loop as well as the players involved in the machinery of the loop are far to be all known. The literature provides plenty of potential regulators whose physiological relevance is more or less ascertained but many pieces are still missing to figure out the process. Our first objective is to get a comprehensive view of MPF activation. -  How do oocytes repress replication during meiosis is a very important question underlying the production of functional gametes and represents the second part of our project. After a single round of pre-meiotic S-phase, oocytes enter meiosis, arrest at prophase I and lose the ability to replicate DNA. Upon hormonal stimulation, arrested oocytes resume meiosis and reestablish DNA replication competence in meiosis I. However, once replication competence is established, DNA replication has to be immediately repressed until fertilization. The mechanisms that repress DNA replication until meiosis is completed are totally unknown. The understanding of this very important feature of meiosis that ensures the ploidy of the future embryo should bring new insights in the interplay between oncogenes and S-phase of the cell cycle. -  This project is based on a physiological model system, the meiotic divisions of Xenopus oocyte, a broadly used paradigm to study MPF activation. The oocytes are physiologically arrested in prophase of the first meiotic division (a G2 phase). They re-enter the first meiotic division in response to progesterone and arrest again at metaphase of the second meiotic division. This G2-M meiotic transition has two main characteristics making this process a great model system. First, these cells are naturally arrested in late G2 and then in M-phase, avoiding any synchronization by pharmacological agents known to produce cell alterations. Second, they are giant cells available in large amounts, allowing easy micromanipulations (such as microinjection) and biochemical approaches. The Xenopus oocyte has therefore emerged as an ongoing pioneer model system, as ascertained by the attribution of the Nobel prize in 2001. Our project includes three experimental programs based on a transdiscipli