X-chromosome inactivation: a historic topic that's still hot.

The last edition of the X-chromosome inactivation (XCI) meeting was held as an EMBO workshop in Berlin on 19-22 June 2023. The conference took place at the Harnack-haus in the Dahlem district, birthplace of the first modern research campus, where notable scientists such as Lise Meitner, Hans Krebs and, briefly, Albert Einstein conducted their research. This special edition, also accessible online, was organized by Rafael Galupa (Centre for Integrative Biology of Toulouse, France), Joost Gribnau (Erasmus MC Rotterdam, The Netherlands), Claire Rougeulle (Université Paris Cité/CNRS, Epigenetics and Cell Fate Center, Paris, France), Edda Schulz (Max Planck Institute for Molecular Genetics, Berlin, Germany) and James Turner (The Francis Crick Institute, London, UK).

PP2A-Cdc55 phosphatase regulates actomyosin ring contraction and septum formation during cytokinesis.

Eukaryotic cells divide and separate all their components after chromosome segregation by a process called cytokinesis to complete cell division. Cytokinesis is highly regulated by the recruitment of the components to the division site and through post-translational modifications such as phosphorylations. The budding yeast mitotic kinases Cdc28-Clb2, Cdc5, and Dbf2-Mob1 phosphorylate several cytokinetic proteins contributing to the regulation of cytokinesis.

PP2A Functions during Mitosis and Cytokinesis in Yeasts.

Protein phosphorylation is a common mechanism for the regulation of cell cycle progression. The opposing functions of cell cycle kinases and phosphatases are crucial for accurate chromosome segregation and exit from mitosis. Protein phosphatases 2A are heterotrimeric complexes that play essential roles in cell growth, proliferation, and regulation of the cell cycle.

Cdc14 activation requires coordinated Cdk1-dependent phosphorylation of Net1 and PP2A-Cdc55 at anaphase onset.

Exit from mitosis and completion of cytokinesis require the inactivation of mitotic cyclin-dependent kinase (Cdk) activity. In budding yeast, Cdc14 phosphatase is a key mitotic regulator that is activated in anaphase to counteract Cdk activity. In metaphase, Cdc14 is kept inactive in the nucleolus, where it is sequestered by its inhibitor, Net1.