Identification and characterization of novel ciliogenic machinery
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Cilia are microtubule-based structures that project from almost every cell in the vertebrate body. In humans, there are two types of cilia, motile, which generate fluid flow across tissues of the ventricles, airway, and oviduct, as well as in propulsion in single cells, and primary, which are responsible for transducing many signaling pathways. Primary and motile cilia are dependent on a bidirectional trafficking process called intraflagellar transport (IFT) in order to bring material into the cilium, which governs their growth, maintenance, and signaling. IFT is mediated by two distinct protein complexes called IFT-A and IFT-B, which function in anterograde and retrograde transport, respectively. In motile cilia, an organization of multiple large protein complexes within the axoneme allow for wave-like motion to be produced. Instrumental to this motility are axonemal dynein arms, large motor protein complexes that slide along microtubule doublets in a coordinated manner to generate bending. Here, I describe two studies regarding ciliogenesis in multiciliated cells, a highly-specialized cell type decorated with dozens of motile cilia. First, I identify ANKRD55 as an IFT-B interactor. I demonstrate that this protein traffics through multiciliated cell axonemes and results in severe developmental defects in its absence. In addition, I describe early insights into the potential role this gene plays in cilia-related human disease. Together, these data suggest that ANKRD55 is a novel member of IFT-B. Second, I characterize the processes that underlie the cytoplasmic assembly of axonemal dynein arms, wherein various chaperones and cytoplasmic factors work in unison to fold and complex dynein arm subunits prior to ciliary transport. Using various imaging methods, I show that the factors responsible for dynein arm assembly localize to non-membrane bound cytoplasmic phase- separations in multiciliated cells, which we term DynAPs (Dynein Assembly Particles). I then demonstrate that machinery involved in phase separation of stress granules is required for formation of DynAPs and recruitment of dynein to axonemes.