Welcome to the first institute seminar of 2021!
Speaker: Sebastian Schultz, PhD, Department of Molecular Cell Biology
Title: "Should I bend or should I go.."
Time: Wednesday, January 27th, 12 o’clock
Place: on zoom - https://uio.zoom.us/j/68986148494
Meeting ID: 612 8814 2884
Compartmentalisation of cellular material in droplet-like structures is a hallmark of liquid-liquid phase separation, but the mechanisms of droplet removal are poorly understood. Evidence suggests that droplets can be degraded by autophagy, a highly-conserved degradation system in which membrane sheets bend to isolate portions of the cytoplasm within double-membrane autophagosomes. Here, we examine how autophagosomes sequester p62/SQSTM1-containing droplets in living cells and demonstrate that double-membrane, autophagosome-like vesicles form at the surface of protein-free droplets in vitro via partial wetting. A minimal physical model shows that droplet surface tension supports the formation of membrane sheets. Further, the model predicts that bending sheets divide droplets for piecemeal sequestration or sequester entire droplets. We find that autophagosomal sequestration is robust to variations in droplet-sheet adhesion. However, the two sides of partially wetted sheets are exposed to different environments, which can determine the bending direction of autophagosomal sheets. By discovering this interplay between the material properties of droplets and membrane sheets, we reveal the mechanisms underpinning droplet autophagy. Further, we uncover a switching mechanism that allows droplets to act as liquid assembly platforms for cytosol-degrading autophagosomes or as specific autophagy substrates. We propose that droplet-mediated autophagy represents a novel class of elasto-capillary driven processes, revealing the importance of wetting in cytosolic organization.