Abstract
Cell polarization allows cells to orient their growth and movement and is integral to cell and tissue morphogenesis in diverse biological contexts. A well characterized model of cell polarization is the budding yeast Saccharomyces cerevisiae. These single-celled fungi undergo polarized growth, which requires directed delivery of biosynthetic components and organelles from the mother cell to the growing daughter cell, or bud. For more than 20-years we have known that a polarized actin cable network directs secretion to allow polarized growth in budding yeast, and yet many of the crucial details of the underlying mechanism behind formation of this polarized actin network have remained unclear. In my thesis work, I have addressed this question and uncovered new functions for the yeast-specific protein, Bud14, in directing polarized cell growth. Bud14 was previously identified as a regulatory subunit of the yeast Protein Phosphatase 1 (PP1/Glc7), and then as a binding partner of Bnr1, one of the two yeast formins (a family of actin-assembly proteins) that assemble the actin cable network. I have used CRISPR/Cas9 to introduce targeted mutations in the BUD14 coding sequence to specifically disrupt sequences involved in its direct interactions with the formin Bnr1 and the phosphatase Glc7. Using this approach, I have found that Bud14-Glc7 interactions are required for regulating cell morphology, whereas Bud14-Bnr1 interactions are not. Furthermore, I identify a new role for Bud14 in controlling the localization and dynamics of the second yeast formin, Bni1, and show that there is a correlation between hyperaccumulation of Bni1 at the cell tip and an elongated cell morphology.