Understanding the function of novel cytoskeletal polymers in the extreme mechanics of eukaryotic cells

The ability of living cells to locomote, generate and resist mechanical forces and spatially organize their contents relies on networks of cytoskeletal proteins. Decades of research have increased our understanding of the mechanisms of assembly and force generation by actin, tubulin, and intermediate filament networks. In contrast, far less is known about other "unconventional" cytoskeletal proteins that form structures that enable dynamic cell shape changes. Centrins are conserved proteins across eukaryotes that form Ca2+ sensitive contractile fibers that underlie the ultrafast deformations observed in free living unicellular protists. These rapid shape changes are thought to result from the contraction of filaments formed by centrin and Sfi1, a flexible scaffold protein that binds centrin to form networks. Here, we visualize centrin networks in the algae Chlamydomonas reinhardtii and the ciliate Paramecium tetraurelia, including mutant strains with altered centrin network architecture, to explore how centrin networks form and how network architecture determines cellular contraction dynamics. Our studies provide new insights into the mechanisms of assembly and force generation of novel cytoskeletal polymers. Beyond their biological significance, our findings will provide blueprints for the design of novel adaptable bioinspired metamaterials capable of withstanding large strains and undergoing extreme elastic deformations.