Molecular and ultrastructural analysis of organelle remodelling and organelle contacts during mitosis

• Applicants: Dr. Anne-Lore Schlaitz; Dr. Yannick Schwab
• Subject Area: Cell Biology
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 564680514

Mitosis is essential for development and tissue homeostasis, and its deregulation may lead to cancer, making it a key challenge to understand how cells safeguard mitotic division. The mitotic fate of chromosomes and their segregation to daughter cells have been studied for decades. However, we know much less about the mechanisms that remodel membrane-bound organelles and ensure their proper inheritance. Organelles have defined shapes and distributions, and they extensively interact with each other through membrane contact sites (MCS), resulting in a complex intracellular architecture. Organelle organization depends on cytoskeletal systems and on MCS. Mitotic cell division therefore requires the coordinated remodelling of organelles, chromosomes, cytoskeletal elements, and likely MCS. However, we lack a comprehensive picture of the intracellular organization of mitotic cells, and the fate of MCS during mitosis has not been systematically investigated yet. Further, the mechanisms mediating mitotic organelle remodelling are incompletely understood. With the proposed work, we aim to obtain quantitative descriptions of organelle morphologies and distributions, and of MCS during mitosis and compare them to the interphase situation. To achieve this, we will use Focused Ion Beam-Scanning Electron Microscopy (FIB-SEM), a volume-EM method that allows to image entire cells at an isotropic resolution of 8 nm. The obtained datasets will be efficiently segmented and analyzed using our recently developed computational tools. After obtaining a quantitative description of intracellular architecture during mitosis, we will investigate the mechanisms that establish this architecture. We will focus on the endoplasmic reticulum (ER) because, during interphase, it forms MCS with all other organelles and impacts their dynamic behavior. Importantly, during mitosis, the ER remains one single network that spans the cytoplasm whereas other complex organelles such as mitochondria and the Golgi complex fragment and disperse. The ER might therefore organize other organelles through MCS during mitosis. To test this hypothesis, we will first characterize proteins that associate with MCS in a cell cycle-specific manner. We will ask whether these candidates mediate the formation of mitosis-specific MCS and contribute to the dynamic behavior and distribution of organelles during mitosis. Additionally, we will query the contribution of ER to mitotic cell organization directly and ask whether ER acts as a scaffold for the organization of other organelles. To this end, we will restructure the mitotic ER in defined ways and move it more centrally or more peripherally through synthetic tethers, and determine whether and how the organization of other organelles changes. Once we uncovered mechanisms establishing it, we can perturb the intracellular organization of mitotic cells to ask how the distinct architecture of a mitotic cell ensures faithful cell division.

• DFG Programme: Research Grants