Elucidating how epithelial cell polarity maintenance safeguards genome stability during cell division.

Polarised epithelial cell divisions represent a critical mechanism for correct partitioning of fate determinants and genomic material into the daughter cells during tissue homeostasis and morphogenesis, and their disruption can lead to severe developmental disorders and diseases such as premature aging and cancer. Yet, the precise mechanisms coordinating cell polarity and correct mitotic spindle dynamics and chromosome segregation fidelity, to ensure proper epithelial integrity and differentiation remain ill defined. In a recent screen, we identified a novel protein complex including the membrane-associated Annexin A1 (ANXA1) protein and its partner S100A11 that interacts with the evolutionarily conserved LGN mitotic complex in mammary epithelial cells. Preliminary observations, show that disruption of ANXA1-S100A11 complex results in defective spindle dynamics and abnormal chromosome segregation, leading to cytokinesis defects and impaired cell-cell adhesion. This collaborative project will provide the PhD student with a cutting-edge multidisciplinary training in cell biology and biotechnology combined with 3D and super-resolution imaging to test the hypothesis that ANXA1-S100A11 coordinates cell polarity, spindle dynamic and faithful chromosome alignment and segregation to ensure epithelial integrity. To specifically study the role of ANXA1-S100A11 complex during mitosis, the PhD candidate will employ CRISPR/Cas9 genome editing to generate mammary epithelial cells expressing endogenously degron-tagged ANXA1 and S100A11 to induce acute protein depletion during cell division. By combining advanced and super-resolution microscopy technology, the PhD student will dissect the role(s) of ANXA1-S100A11 complex in the coordination of the dynamics of cell-cell adhesion molecules, LGN spindle orientation machinery and chromosome stability regulators (also identified in our screen) in a nanoscale. The PhD student will further extend the study in stem cell-derived mammary 3D organoids combined with 3D confocal imaging to assess the impact of ANXA1-S100A11-loss-mediated defects on epithelial integrity and differentiation during morphogenesis.
This project will provide a significant mechanistic insight on how ANXA1-S100A11 (probably the first characterised protein complex) bridges cell polarity control and chromosome stability maintenance to ensure proper epithelial architecture and prevent malignant transformation. Our findings will be used for more ambitious proposals for BBSRC or MRC project grants, using mouse and mathematical models to investigate how disruption of these mechanisms in vivo can contribute to premature aging and cancer.