Topological brakes in an ultrafast giant cell

Understanding extremes in biology provides novel insights into the fundamental limits of life. To study cellular adaptations under extreme forces, we study the ultrafast contractions (50% body length contraction within 5-10 msec, peak acceleration 15g) in Spirostomum ambiguum, a giant single cell organism, as a model system. Utilizing TEM and confocal imaging, we discover a novel fenestrated cubic membrane architecture of rough endoplasmic reticulum (RER) wrapping around vacuolar meshwork, forming a 3D sheet spanning the entire cell. We explore the mechanical role of the entangled architecture to understand how giant cells dissipate energy in such a short time scale. We use a simple model with an overdamped molecular dynamics scheme where the RER-vacuolar meshwork is captured as hard particles entangled with inextensible strings, undergoing large deformation. Our simulations reveal that the topological confinement can induce jamming at a volume fraction significantly below critical value and dissipate more energy while preserving spatial relationship among vacuoles. Our findings suggest a new role of RER-vacuolar meshwork in a giant cell, which can be considered a metamaterial that applies topological brakes and preserves organelle architecture under extreme motility events.