Abstract
Tight coordination of the actin and microtubule cytoskeletons is required for diverse cellular processes, such as maintaining cellular morphology and motility. These active biological polymers consume energy in order to assemble into different types of cellular structures, i.e., filaments, bundles, or branched arrays. However, there is relatively little known about how the dynamics of the two systems are coordinated. Recent results in the Goode lab show that the microtubule plus end-binding protein CLIP-170 directly regulates formin-mediated actin polymerization through a conserved sequence motif, providing a new link between actin and microtubule dynamics. In yeast, the homolog of CLIP-170, called Bik1, has been shown to regulate microtubule dynamics, and to localize to microtubules. In my thesis work, I examined whether the formin regulation activity of mammalian CLIP-170 also extends to Bik1in budding yeast. I have tested whether purified Bik1 can regulate the in vitro actin assembly activities of the two yeast formins, Bnr1 and Bni1, and found that it specifically inhibits Bnr1-mediated elongation and nucleation. This inhibition is dependent on the FH1 domain of Bnr1. I have imaged bik1Δ cells to identify actin cable defects or related phenotypes, and found that they are enlarged, have more cables than wild type cells, and their cables are more disorganized. Finally, I have observed the dynamic localization and behavior of Bik1-3GFP in live cells using spinning disc confocal microscopy. Future in vivo and in vitro analyses will help elucidate to what extent formin regulation by CLIP-170 is conserved across evolution.