Genetic Mechanisms of Multiciliated Cell Development during Renal Ontogeny

For many years, cilia have been appreciated for their role in signal transduction, serving as antennas for mechanosensory cascades and highways of protein transport. Additionally, cilia dysfunction results in excess fluid accumulation and aberrant particle displacement responsible for a variety of diseases and larger syndromes, collectively known as ciliopathies. As such, the functions and anatomical structure of cilia have been carefully characterized. While primary and motile cilia vary in microtubule arrangement, their core roles remain highly conserved across vertebrates. Consequently, vertebrate models of ciliogenesis span a wide range of species and tissues, including the zebrafish pronephros, or embryonic kidney. Aside from optical transparency and large clutch size, the zebrafish pronephros presents a functionally conserved and anatomically simple model to examine ciliogenesis. In zebrafish, the pronephros is comprised of two linear nephrons that are fully formed and organized in functionally distinct segments of mono-ciliated transporter cells by just 24 hours post fertilization, or the 28 somite stage. The arrangement of these segments is highly conserved to that of the mammalian nephron, the smallest functional unit of the vertebrate kidney. In addition to the transporter cells, the zebrafish pronephros houses a second epithelial population of multiciliated cells (MCCs). MCCs are a highly specialized and conserved cell type that is characterized by apical bundles of motile cilia. In the pronephros, MCCs are dispersed in a “salt-and-pepper” like fashion and function in fluid propulsion through the nephron tubule. Disrupted multiciliogenesis can lead to hydrocephaly, respiratory disease and infertility in humans, and the abnormal presence of MCCs in renal biopsies of patient’s with kidney disease has been observed in a handful of cases. This dissertation will describe reverse and chemical genetic approaches that revealed novel insights into the genetic mechanisms of MCC development in the zebrafish pronephros. In short, the work presented here uncovered an integrated network of etv5a, etv4, irx2a, and prostaglandin signaling in the specification and maturation of renal MCCs. These findings demonstrate the fecundity of using the zebrafish pronephros as a model to examine multiciliogenesis in vivo, enhancing our knowledge of the complex process of MCC ontogeny that will further increase understanding the connection between cilia dysfunction and disease in vertebrates.