Deciphering how directional cues are relayed into polarized collective cell migration

About This Grant

Project Summary Cells within epithelial sheets undergo collective cell migration during a variety of processes including tissue morphogenesis, organ homeostasis, and cancer metastasis. However, we lack a clear understanding of how epithelial collectives sense directional cues and translate them into polarized movements, particularly in vertebrates. Through the proposed project, I will establish the zebrafish pronephros (embryonic kidney) as a tractable, in vivo model of epithelial collective cell migration. During development, the epithelial cells of the pronephric duct undergo a collective cell migration towards the anterior of the embryo, driving morphogenesis of the proximal tubule. This migration is powered by the extension and retraction of migratory protrusions at the basal cell surface. Lumenal fluid flow has been identified as the directional cue that dictates migration orientation: pronephric epithelial cells migrate against flow. Therefore, the pronephric epithelium is an ideal yet underutilized system to study how cells sense and relay directional information during collective migration, as both the upstream polarizing cue (fluid flow) and the downstream readout (anterior migration) are known. Collective migration is often regulated by polarity modules that coordinate cytoskeletal behaviors. I hypothesize that the zebrafish Fat1a/LarA/LarB proteins function as a migratory polarity module that orients pronephric protrusions in a flow-dependent manner. In Aim 1, I will test this hypothesis through live-imaging of migration in wildtype and polarity-mutant embryos. By mechanically altering pronephric flow in embryos expressing tagged polarity proteins, I will determine if the Fat1a/LarA/LarB polarity module localizes in a flow-dependent manner. Cilia have long been speculated to function as flow sensors in the pronephric epithelium. I hypothesize that mechanosensitive sensory cilia detect flow via the Pkd2/calcium signaling pathway. In Aim 2, I will test this hypothesis by performing live calcium imaging to ascertain if there is a population of cilia exhibiting flow- responsive calcium signaling. Engineering of a ciliary-trafficking Pkd2-mutant will reveal if ciliary Pkd2 is required for migration. Together, the proposed experiments will shed light on how epithelial cells translate directional cues into polarized migration, advancing our understanding of kidney development. Moreover, through completion of these aims, I will learn essential skills in zebrafish genetics, molecular cloning, and live-imaging that will be key to the success of my future independent research lab.