Browsing by Subject "Formin"

Essential and diverse biological processes such as cell division, morphogenesis and migration are regulated by a family of molecular switches called Rho GTPases. These proteins cycle between active, GTP-bound states and inactive, GDP-bound state and this cycle is regulated by families of proteins called Rho GEFs and GAPs. GAPs are proteins that stimulate the intrinsic GTPase activity of Rho-family proteins, potentiating the active to inactive transition. GAPs target specific spatiotemporal pools of GTPases by responding to cellular cues and utilizing protein-protein interactions. By dissecting these interactions and pathways, we can infer and then decipher the biological functions of these GAPs.

This work focuses on the characterization of a novel Rho-family GAP called srGAP2. In this study, we identify that srGAP2 is a Rac-specific GAP that binds a Formin-family member, Formin-like 1 (FMNL1). FMNL1 is activated by Rac and polymerizes, bundles and severs actin filaments. srGAP2 specifically inhibits the actin severing of active FMNL1, and the assembly of an srGAP2-FMNL1 complex is regulated by Rac. Work on FMNL1 shows that it plays important roles in regulating phagocytosis and adhesion in macrophages. To learn more about srGAP2 and its role in regulating FMNL1, we studied macrophages isolated from an srGAP2 KO mouse we have recently generated. This has proven quite fruitful: loss of srGAP2 decreases the ability for macrophages to invade through extracellular matrix but increases phagocytosis. These results suggest that these two processes might be coordinated in vivo by srGAP2 and that srGAP2 might be a critical regulator of the innate immune system.

Tip growth in fungi involves highly polarized secretion and modification of the cell wall at the growing tip. The genetic requirements for initiating polarized growth are perhaps best understood for the model budding yeast, Saccharomyces cerevisiae. Once the cell is committed to enter the cell cycle by activation of G1 cyclin/cyclin-dependent kinase (CDK) complexes, the polarity regulator Cdc42 becomes concentrated at the presumptive bud site, actin cables are oriented towards that site, and septin filaments assemble into a ring around the polarity site. Several minutes later, the bud emerges. Here, we investigated the mechanisms that regulate the timing of these events at the single cell level and the role of polarisome during pheromone-induced polarized growth. We employed genetics and live cell microscopy to characterize cellular events. Septin recruitment was delayed relative to polarity establishment, and our findings suggest that a CDK-dependent septin “priming” facilitates septin recruitment by Cdc42. Bud emergence was delayed relative to the initiation of polarized secretion, and our findings suggest that the delay reflects the time needed to weaken the cell wall sufficiently to bud. Rho1 activation by Rom2 occurred at around the time of bud emergence, perhaps in response to local cell wall weakening. This report reveals regulatory mechanisms underlying the morphogenetic events in the budding yeast.