Genetic dissection of fluid flow signaling in Left-Right patterning of zebrafish

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Project Summary/Abstract Fluid flow transduction pathways are critical for development, however it is little known how cells sense and transduce fluid flow signals. Defects in flows and flow sensation result in developmental diseases including primary ciliary dyskinesia, heterotaxy, and congenital heart disease. While the Polycystin transmembrane proteins have been implicated in fluid flow sensation and transduction, few other proteins regulating flow sensation and transduction have been identified. This study aims to characterize novel flow sensory pathway regulators and build on the Polycystin flow sensory complex using the highly tractable left-right (L-R) patterning system of zebrafish embryos. In this system an asymmetric fluid flow is sensed by ciliated cells and breaks L-R symmetry by repressing a key target gene, dand5, leading to asymmetric expression of downstream genes. To identify flow sensory pathway components in the L-R patterning system, I performed a reverse genetics screen and identified several novel regulators. Focusing on four of these, my overarching hypothesis is that they function as part of flow signal sensation or transduction, upstream of dand5 repression. I will test this hypothesis through two Specific Aims: 1) Test the requirement of novel regulators for cilia formation, motility, flow generation and flow sensory pathway output using a novel pathway sensor I am building and 2) Test the hypothesis that pkhd1l1, or Fibrocystin, functions in flow sensation in cilia as part of the Polycystin complex. Overall, this work will expand our understanding of flow sensory pathways by mechanistically placing novel regulators into the L-R patterning pathway. Moreover, this work aims to build on the current Polycystin flow sensory complex by dissecting Polycystin-Fibrocystin interactions, something which will have implications for L-R patterning and kidney diseases.