Hydraulics of cellular extension and contraction in Lacrymaria olor

Cells dynamically change shape and form to adapt to various functions. Amongst the fastest cellular movements are “neck” extensions of a unicellular protist, Lacrymaria olor, which changes its morphology in milliseconds in order to hunt for prey. These neck extensions are powered by motile cilia while the cortical helical cytoskeleton provides a structural architecture capable of supporting cellular extensions ranging from 10 to 20 body lengths in a few seconds. This unique transformation provides a framework for studying cellular hydraulics - flow of cytoplasmic content at rapid pace. Surprisingly, experimental measurements indicate that common organelles do not flow into the neck - implying a cytoplasmic phase separation between neck and body. Via theory and experiments, we demonstrate that a poroelastic cytoplasm enables these fast movements while protecting cellular architectures. Our current work provides a new approach for exploring extreme dynamical shape changes in eukaryotic cells.