Reiter, J. F. | bioRxiv Science

bioRxiv2017

Evolutionary proteomics uncovers ciliary signaling components

Cilia are organelles specialized for movement and signaling. To infer when during animal evolution signaling pathways became associated with cilia, we characterized the proteomes of cilia from three organisms: sea urchins, sea anemones and choanoflagellates. From these ciliomes, we identified 437 high confidence ciliary candidate proteins conserved in mammals, including known regulators of Hh, GPCR and TRP channel signaling. The phylogenetic profiles of their ciliary association indicate that the Hh and GPCR pathways were linked to cilia before the origin of bilateria and TRP channels before the origin of animals. We demonstrated that some of the candidates not previously implicated in ciliary biology localized to cilia and further investigated ENKUR, a TRP channel-interacting protein that we identified in the cilia of all three organisms. In animals, ENKUR is expressed by cells with motile cilia, ENKUR localizes to cilia in diverse organisms and, in both Xenopus laevis and mice, ENKUR is required for patterning the left/right axis. Moreover, mutation of ENKUR causes situs inversus in humans. Thus, proteomic profiling of cilia from diverse eukaryotes defines a conserved ciliary proteome, reveals ancient connections to Hh, GPCR and TRP channel signaling, and uncovers a novel ciliary protein that controls vertebrate development and human disease.

evolutionary biology↗

bioRxiv2017

Super-Resolution Microscopy Reveals That Disruption Of Ciliary Transition Zone Architecture Is A Cause Of Joubert Syndrome

Diverse human ciliopathies, including nephronophthisis (NPHP), Meckel syndrome (MKS) and Joubert syndrome (JBTS), can be caused by mutations affecting components of the transition zone, a ciliary domain near its base. The transition zone controls the protein composition of the ciliary membrane, but how it does so is unclear. To better understand the transition zone and its connection to ciliopathies, we defined the arrangement of key proteins in the transition zone using two-color stochastic optical reconstruction microscopy (STORM). This mapping revealed that NPHP and MKS complex components form nested rings comprised of nine-fold doublets. The NPHP complex component RPGRIP1L forms a smaller diameter transition zone ring within the MKS complex rings. JBTS-associated mutations in RPGRIP1L disrupt the architecture of the MKS and NPHP rings, revealing that vertebrate RPGRIP1L has a key role in organizing transition zone architecture. JBTS-associated mutations in TCTN2, encoding an MKS complex component, also displace proteins of the MKS and NPHP complexes from the transition zone, revealing that RPGRIP1L and TCTN2 have interdependent roles in organizing transition zone architecture. To understand how altered transition zone architecture affects developmental signaling, we examined the localization of the Hedgehog pathway component SMO in human fibroblasts derived from JBTS-affected individuals. We found that diverse ciliary proteins, including SMO, accumulate at the transition zone in wild type cells, suggesting that the transition zone is a way station for proteins entering and exiting the cilium. JBTS-associated mutations in RPGRIP1L disrupt SMO accumulation at the transition zone and the ciliary localization of SMO. We propose that the disruption of transition zone architecture in JBTS leads to a failure of SMO to accumulate at the transition zone, disrupting developmental signaling in JBTS.

cell biology↗