Wet scissors: How biomolecular condensates cut cellular membranes

Membrane shape is a fundamental determinant of cellular organisation. Reshaping of membranes is crucial for dynamic processes including organelle and cell division, endocytosis and membrane trafficking. Membrane fission (or scission) is a discontinuous, topological shape change that is central in many such processes. Specialised remodelling proteins, such as dynamins and ESCRT proteins, are capable of forming oligomeric spirals that drive membrane fission in cells. In this review, we summarise evidence demonstrating that capillary forces generated by liquid-like biomolecular condensates can facilitate cellular membrane reshaping and drive fission events. We draw on our recent findings that condensates are implicated in multivesicular body formation to describe the molecular and physical principles that allow biomolecular condensates to cut membranes. We further discuss possible interactions between novel condensate-mediated fission processes and established reshaping processes. We propose that condensates make an important contribution to membrane remodelling events involved in the biogenesis of diverse cellular structures. The characterisation of condensate-mediated membrane reshaping promises to transform our understanding of intracellular organisation and dynamics.