Cilia are microtubule-based organelles that mediate signal transduction in a variety of tissues. Despite their importance, the signaling cascades that regulate cilia formation remain incompletely understood. Here we report that prostaglandin signaling affects ciliogenesis by regulating anterograde intraflagellar transport (IFT). Zebrafish leakytail (lkt) mutants display ciliogenesis defects, and lkt locus encodes an ATP-binding cassette transporter (ABCC4). We show that Lkt/ABCC4 localizes to the cell membrane and exports prostaglandin E2 (PGE2), a function that is abrogated by the Lkt/ABCC4T804M mutant. PGE2 synthesis enzyme Cyclooxygenase-1 and its receptor, EP4, which localizes to the cilium and activates cAMP-mediated signaling cascade, are required for cilia formation and elongation. Importantly, PGE2 signaling increases anterograde but not retrograde velocity of IFT and promotes ciliogenesis in mammalian cells. These findings lead us to propose that Lkt/ABCC4-mediated PGE2 signaling acts through a ciliary G-protein-coupled receptor, EP4, to upregulate cAMP synthesis and increase anterograde IFT, thereby promoting ciliogenesis
