The Forth lab is currently working to understand how the cell builds the complex machinery needed to divide. We are particularly interested in understanding how ensembles of proteins, which are each only several nanometers big, cooperate to build structures that are thousands of times their size (microns), and to understand how forces and motions within the cell are regulated. We have recently been very interested in a non-motor protein, called PRC1, that crosslinks microtubules to form higher-order bundles. We have shown that PRC1 generates viscous resistive forces that (1) increase as microtubule filaments slide faster and (2) increase with a higher concentration of PRC1 crosslinks. We have also demonstrated that PRC1 can form clusters under tension that further stabilize the microtubule bundles and clarify how stable anaphase central spindles are built. We have also recently collaborated with the Al-Bassam lab at UC Davis to show that the tail domain of Eg5 is required for efficient generation of microtubule sliding forces, a finding that has implications for bipolar spindle assmebly in mammalian cells.