Hosts: Laura Buttitta & Tim James

Abstract: Eukaryotic cells often use their actin cytoskeleton for multiple functions at the same time. For example, the actin networks of human epithelial cells can simultaneously control cell migration, endocytosis, vesicular trafficking, cell polarity, and other actin functions important for human health. Despite having distinct functions, individual actin networks share structural components and regulators, including polymerization factors, polymer bundlers, and proteins that promote network turnover. Determining how cells control different subsets of actin functions, and how these functions change over time, are difficult questions to address given the large amount of molecular overlap and spatial proximity between functionally distinct actin networks in animal cells. Budding and fission yeasts—the other most commonly-used model systems to study actin—have spatially separated actin networks, a property that has made them powerful for determining precise molecular mechanisms underlying actin-dependent functions like endocytosis. Yeast, however, have lost important actin structures including an actin cortex and protrusions used for cell motility. Yeasts are also missing many important regulators of human actin networks, making it difficult to determine to what extent the rules of actin network specification of yeast can be applied to animal cells. To bridge this gap, my lab uses chytrid fungi as a system to study the functional specification of animal-like and yeast-like actin networks because: (a) chytrids are early-branching fungi and have retained actin regulators found in human cells that have been lost by yeast and other fungi as well as fungal-specific actin network components (1), and (b) chytrids undergo natural developmental transitions between motile, animal-like cell types with an actin cortex and sessile, yeast-like cell types with cell walls and physically separated actin networks. In this seminar, I will explain how we came to study these fascinating fungi and how we are now using chytrid fungi as a system to study the functional specification of animal-like and yeast-like actin networks and the developmental transitions between them.