Cell shape is intimately tied to cell function. The skeleton of a cell, called the cytoskeleton, is made of a network of polymers, which drive shape changes. The dynamic assembly and rearrangement of the cytoskeleton allow cells to react in both time and space to specific signals. A fundamental challenge for a cell is that the molecules of the cytoskeleton are much smaller than the size of the whole cell. A goal of this project is to understand how information about scale is transmitted in a cell so that small building blocks (nanometer in size) can carry out shape changes that are orders of magnitude larger. This work will reveal the scaling blueprint for one part of the cytoskeleton. The experiments will determine how structures built from filaments coming together in different arrangements and patterns leads to differences in cell shape and function. This work is important because it will reveal basic principals of self-assembly in living systems. Understanding these principals is essential to design synthetic cells that will likely be used for solving a variety of current and future problems such as in computing, bioenergy or bioremediation.
The septin cytoskeleton is an especially powerful polymer network to analyze how cells scale and shape protein structures because septins assemble into diverse forms in cells. Septin filaments can be knit together into bundles, gauzes, rings and lattices depending on the cell context. These different forms can be hundreds of nanometers to micrometers in size. In many cases these assemblies form on membrane surfaces where they function as scaffolds and membrane barriers. It is not understood how assemblies of such varied geometry and size can be built out of the same fundamental building block of a septin filament. The objectives of this study address how cells regulate septins to build structures of versatile form and function. These objectives will be achieved through biophysical approaches, optogenetics and cell-free reconstitution. Cutting-edge, quantitative imaging will be employed including single-molecule and polarization fluorescence microscopy, high-speed atomic force microscopy together with cell free reconstitution and mathematical modeling. Septins are nearly ubiquitous in eukaryotes and yet there are major gaps in understanding how cells construct higher-order structures from septin filaments. The ultimate goal is to understand how variable function emerges from this variation in form. The experiments here address problems that are fundamental to how all cells are spatially organized as there are many examples of micrometer-scale assemblies that are built from nanometer-sized building blocks.
