Project Summary/Abstract Many cells possess projections from their surfaces called cilia. Mouse genetics has been instrumental in uncovering novel requirements for cilia in development, such as left/right axis specification, and skeletal and neural tube patterning. During mammalian development, cilia generate and sense flow, and interpret intercellular cues, such as Hedgehog signals. Defects in ciliary function in humans cause diverse diseases known as ciliopathies. Despite the importance of the cilium, fundamental aspects of ciliary biology, including how cilia are constructed, how they signal, and how they coordinate diverse developmental events, remain poorly understood. To illuminate answers to these longstanding questions, we propose to make use of a unique resource, the knockout mouse mutant strains being created by the International Mouse Phenotyping Consortium (IMPC). We have developed an innovative algorithm and demonstrated that it can identify mutant lines for which ciliary analysis will be valuable. We will use this algorithm to select mutants, and use these mutants to answer three complementary questions about cilia: 1) How are the sophisticated structures and subdomains of cilia built and contribute to ciliary function? 2) How is ciliary motility established and regulated? 3) How do cilia transduce intracellular signals, such as Hedgehog signals, and how does loss of this intercellular communication contribute to the pathogenesis of ciliopathies? To address these questions, we will combine advanced imaging approaches, including super-resolution microscopy, micro-computed tomography, with novel genetic tools such as transgenes that label cilia with GFP. The expertise accrued during our combined 25 years working on cilia in mouse development will allow us to use the novel mouse mutants to uncover novel principles underlying ciliogenesis and ciliary signaling. These discoveries will help identify the causative genes for orphan diseases, and illuminate the developmental origins of human ciliopathies.