Description du sujet de thèse

Role of non-canonical cyclin B3 in meiosis and mitosis in Phallusia and Clytia

Contexte de travail

The project will be led by Stefania Castagnetti (Mitosis and Spindle Control team), in collaboration with Evelyn Houliston (Developmental Mechanisms of Cnidarians team). Both teams are based at the Laboratoire de Biologie du Développement de Villefranche (LBDV) and have long been interested in cell cycle regulation, oocyte biology, and early embryogenesis in ascidians (Castagnetti team) and cnidarians (Houliston team). Both teams have the expertise and know-how necessary to carry out the project. State-of-the-art equipment for biochemistry, molecular biology, and microscopy, as well as animal facilities, are available on site.
Assigned activities:
Eukaryotic cell division cycles are regulated by phosphorylation, with the cellular proteins responsible for M phase progression being universally phosphorylated by the Cdk1-Cyclin B complex. This project examines how the cell cycle mechanism has adapted to regulate meiotic divisions in the specific context of female animal meiosis. It focuses on the role of Cyclin B3, recently identified as an essential regulator of oocyte meiosis in vertebrates. In mice and Xenopus, the degradation of Cyclin B3 after meiosis I (MI) prevents progression to the second meiotic division, causing oocytes to arrest in MII to await sperm entry. Although cyclin B3 is highly conserved in animals, this role in meiotic arrest in MI is specific to vertebrates, as oocytes in non-vertebrate species arrest at other stages of meiosis. The objective of the PhD project is to understand the role of cyclin B3 during meiosis and early embryonic divisions in the sea squirt Phallusia mammillata and the jellyfish Clytia hemisphaerica. The student will determine the protein expression profiles of canonical cyclins B1/2 and B3 during meiosis and mitosis using antibodies customized. In order to distinguish the contributions of protein synthesis and degradation to the identified profiles of the two cyclin B proteins, the dynamics of degradation will be analyzed in vivo using quantitative imaging after injection of mRNA encoding fluorescently labeled cyclin B3 and specific inhibitors of degradation and/or translation. The student will also analyze the function of cyclin B3 in meiosis and mitosis by manipulating protein levels, either by reducing them using specific morpholinos or shRNAs, or by overexpressing them through injection of specific in vitro transcribed mRNAs. Finally, specific targets of CDK/cyclin B3 will be identified using a phosphoproteomic approach.