Active transport and diffusion barriers restrict Joubert Syndrome-associated ARL13B/ARL-13 to an Inv-like ciliary membrane subdomain

PLoS Genet. 2013;9(12):e1003977. doi: 10.1371/journal.pgen.1003977. Epub 2013 Dec 5.


Cilia are microtubule-based cell appendages, serving motility, chemo-/mechano-/photo- sensation, and developmental signaling functions. Cilia are comprised of distinct structural and functional subregions including the basal body, transition zone (TZ) and inversin (Inv) compartments, and defects in this organelle are associated with an expanding spectrum of inherited disorders including Bardet-Biedl syndrome (BBS), Meckel-Gruber Syndrome (MKS), Joubert Syndrome (JS) and Nephronophthisis (NPHP). Despite major advances in understanding ciliary trafficking pathways such as intraflagellar transport (IFT), how proteins are transported to subciliary membranes remains poorly understood. Using Caenorhabditis elegans and mammalian cells, we investigated the transport mechanisms underlying compartmentalization of JS-associated ARL13B/ARL-13, which we previously found is restricted at proximal ciliary membranes. We now show evolutionary conservation of ARL13B/ARL-13 localisation to an Inv-like subciliary membrane compartment, excluding the TZ, in many C. elegans ciliated neurons and in a subset of mammalian ciliary subtypes. Compartmentalisation of C. elegans ARL-13 requires a C-terminal RVVP motif and membrane anchoring to prevent distal cilium and nuclear targeting, respectively. Quantitative imaging in more than 20 mutants revealed differential contributions for IFT and ciliopathy modules in defining the ARL-13 compartment; IFT-A/B, IFT-dynein and BBS genes prevent ARL-13 accumulation at periciliary membranes, whereas MKS/NPHP modules additionally inhibit ARL-13 association with TZ membranes. Furthermore, in vivo FRAP analyses revealed distinct roles for IFT and MKS/NPHP genes in regulating a TZ barrier to ARL-13 diffusion, and intraciliary ARL-13 diffusion. Finally, C. elegans ARL-13 undergoes IFT-like motility and quantitative protein complex analysis of human ARL13B identified functional associations with IFT-B complexes, mapped to IFT46 and IFT74 interactions. Together, these findings reveal distinct requirements for sequence motifs, IFT and ciliopathy modules in defining an ARL-13 subciliary membrane compartment. We conclude that MKS/NPHP modules comprise a TZ barrier to ARL-13 diffusion, whereas IFT genes predominantly facilitate ARL-13 ciliary entry and/or retention via active transport mechanisms.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • ADP-Ribosylation Factors / genetics*
  • ADP-Ribosylation Factors / metabolism
  • Abnormalities, Multiple
  • Animals
  • Bardet-Biedl Syndrome / genetics
  • Bardet-Biedl Syndrome / pathology
  • Biological Transport, Active / genetics
  • Caenorhabditis elegans / genetics*
  • Caenorhabditis elegans / metabolism
  • Cerebellar Diseases / genetics*
  • Cerebellar Diseases / pathology
  • Cerebellum / abnormalities
  • Cilia / genetics*
  • Cilia / metabolism
  • Ciliary Motility Disorders / genetics
  • Ciliary Motility Disorders / pathology
  • Cytoskeletal Proteins / genetics
  • Cytoskeletal Proteins / metabolism
  • Encephalocele / genetics
  • Encephalocele / pathology
  • Eye Abnormalities / genetics*
  • Eye Abnormalities / pathology
  • Humans
  • Kidney Diseases, Cystic / genetics*
  • Kidney Diseases, Cystic / pathology
  • Membranes / metabolism
  • Polycystic Kidney Diseases / genetics
  • Polycystic Kidney Diseases / pathology
  • Retina / abnormalities*
  • Retina / pathology
  • Retinitis Pigmentosa
  • Transcription Factors / genetics
  • Transcription Factors / metabolism


  • Cytoskeletal Proteins
  • IFT74 protein, human
  • INVS protein, human
  • Transcription Factors
  • ADP-Ribosylation Factors
  • Arl13b protein, human

Supplementary concepts

  • Agenesis of Cerebellar Vermis
  • Meckel syndrome type 1
  • Nephronophthisis 3

Grant support

This work was supported by a Science Foundation Ireland President of Ireland Young Researcher Award (06/Y12/B928 to OEB), the European Community's Seventh Framework Programmes FP7/2009 under grant agreement no: 241955 (SYSCILIA, to MU HK RR OEB) and FP7/2011 under grant agreement no: 278568 (PRIMES, to KB MU), the Kerstan foundation (to MU), the Netherlands Organization for Scientific Research (NWO Vidi-91786396 and Vici-016.130.664 to RR), the Foundation Fighting Blindness (C-CMM-0811-0546-RAD02 to RR and C-CMM-0811-0547-RAD03 to HK), research grants from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan (to KK TK), and an IRSCET award (Irish Research Council for Science, Engineering and Technology PhD fellowship to LC). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.