A timeline for C. elegans ciliogenesis. Centriole and ciliary architecture at key stages in the C. elegans life cycle. In contrast to the singlet centrioles in the early embryo (Wolf et al., 1978; Pelletier et al., 2006), centrioles in sensory neurons possess doublet microtubules (MTs). Within 1 h after terminal cell division (twofold stage; 490 min after fertilization), centrioles have docked to the plasma membrane and have begun assembling transition zone structures (Y-links and central cylinder). Expansion of transition zone structures requires another hour (threefold stage; 550 min; not depicted). IFT-dependent axoneme extension continues through the larval stages. Centriole degeneration begins with loss of the cartwheel/central tube (by twofold stage), followed by loss of the centriolar microtubule wall component SAS-4 (threefold stage). Centrioles are therefore not directly involved in later events including transition zone expansion and axoneme elongation. HYLS-1 remains on the centriolar remnant and is required for the initial DYF-19/Fbf1-dependent recruitment of IFT components. However, HYLS-1 is dispensable for continued IFT trafficking.