Cep164 provides a molecular link between the mother centriole and the ciliary membrane biogenesis machinery by interacting with the GEF Rabin8 and the GTPase Rab8.

The transition zone (TZ) ciliary subcompartment is thought to control cilium composition and signaling by facilitating a protein diffusion barrier at the ciliary base, and TZ defects cause ciliopathies such as Meckel-Gruber syndrome (MKS), nephronophthisis (NPHP) and Joubert syndrome (JBTS) 1. However, the molecular composition and mechanisms underpinning TZ organisation and barrier regulation are poorly understood. To uncover candidate TZ genes, we employed bioinformatics (co-expression and co-evolution) and identified TMEM107 as a TZ protein mutated in oral-facial-digital syndrome (OFD) and JBTS patients. Mechanistic studies in Caenorhabditis elegans showed TMEM107 controls ciliary composition and functions redundantly with NPHP4 to regulate cilium integrity, TZ docking and assembly of membrane to microtubule Y-link connectors. Furthermore, nematode TMEM107 occupies an intermediate layer of the TZ-localised MKS module by organising recruitment of ciliopathy proteins MKS1, TMEM231 (JBTS20) and TMEM237 (JBTS14). Finally, MKS module membrane proteins are immobile and super-resolution microscopy (STED, dSTORM) in worms and mammalian cells reveals periodic localisations within the TZ. This work expands the MKS module of ciliopathy-causing TZ proteins associated with diffusion barrier formation and provides insight into TZ subdomain architecture.

A functional screen identified MARK4 as a positive regulator of axonemal extension and ciliogenesis via its interaction with the mother centriolar protein ODF2.

The centriolar satellite protein SSX2IP mediates recruitment of Cep290 to the basal body of cilia. It promotes BBSome and Rab8 entry into cilia, as well as accumulation of the ciliary membrane protein SSTR3. The data establish SSX2IP as a novel targeting factor for ciliary membrane proteins cooperating with Cep290, the BBSome, and Rab8.

BackgroundJoubert syndrome (JBTS) and related disorders are defined by cerebellar malformation (molar tooth sign), together with neurological symptoms of variable expressivity. The ciliary basis of Joubert syndrome related disorders frequently extends the phenotype to tissues such as the eye, kidney, skeleton and craniofacial structures.ResultsUsing autozygome and exome analyses, we identified a null mutation in KIAA0556 in a multiplex consanguineous family with hallmark features of mild Joubert syndrome. Patient-derived fibroblasts displayed reduced ciliogenesis potential and abnormally elongated cilia. Investigation of disease pathophysiology revealed that Kiaa0556-/- null mice possess a Joubert syndrome-associated brain-restricted phenotype. Functional studies in Caenorhabditis elegans nematodes and cultured human cells support a conserved ciliary role for KIAA0556 linked to microtubule regulation. First, nematode KIAA0556 is expressed almost exclusively in ciliated cells, and the worm and human KIAA0556 proteins are enriched at the ciliary base. Second, C. elegans KIAA0056 regulates ciliary A-tubule number and genetically interacts with an ARL13B (JBTS8) orthologue to control cilium integrity. Third, human KIAA0556 binds to microtubules in vitro and appears to stabilise microtubule networks when overexpressed. Finally, human KIAA0556 biochemically interacts with ciliary proteins and p60/p80 katanins. The latter form a microtubule-severing enzyme complex that regulates microtubule dynamics as well as ciliary functions.ConclusionsWe have identified KIAA0556 as a novel microtubule-associated ciliary base protein mutated in Joubert syndrome. Consistent with the mild patient phenotype, our nematode, mice and human cell data support the notion that KIAA0556 has a relatively subtle and variable cilia-related function, which we propose is related to microtubule regulation.Electronic supplementary materialThe online version of this article (doi:10.1186/s13059-015-0858-z) contains supplementary material, which is available to authorized users.

Cilia are microtubule-based organelles extending from a basal body at the surface of eukaryotic cells. Cilia regulate cell and fluid motility, sensation and developmental signaling, and ciliary defects cause human diseases (ciliopathies) affecting the formation and function of many tissues and organs. Over the past decade, various Rab and Rab-like membrane trafficking proteins have been shown to regulate cilia-related processes such as basal body maturation, ciliary axoneme extension, intraflagellar transport and ciliary signaling. In this review, we provide a comprehensive overview of Rab protein ciliary associations, drawing on findings from multiple model systems, including mammalian cell culture, mice, zebrafish, C. elegans, trypanosomes, and green algae. We also discuss several emerging mechanistic themes related to ciliary Rab cascades and functional redundancy.

Rab and Arl guanine nucleotide‐binding (G) proteins regulate trafficking pathways essential for the formation, function and composition of primary cilia, which are sensory devices associated with Sonic hedgehog (Shh) signalling and ciliopathies. Here, using mammalian cells and zebrafish, we uncover ciliary functions for Rab35, a multitasking G protein with endocytic recycling, actin remodelling and cytokinesis roles. Rab35 loss via siRNAs, morpholinos or knockout reduces cilium length in mammalian cells and the zebrafish left‐right organiser (Kupffer's vesicle) and causes motile cilia‐associated left‐right asymmetry defects. Consistent with these observations, GFP‐Rab35 localises to cilia, as do GEF (DENND1B) and GAP (TBC1D10A) Rab35 regulators, which also regulate ciliary length and Rab35 ciliary localisation. Mammalian Rab35 also controls the ciliary membrane levels of Shh signalling regulators, promoting ciliary targeting of Smoothened, limiting ciliary accumulation of Arl13b and the inositol polyphosphate 5‐phosphatase (INPP5E). Rab35 additionally regulates ciliary PI(4,5)P2 levels and interacts with Arl13b. Together, our findings demonstrate roles for Rab35 in regulating cilium length, function and membrane composition and implicate Rab35 in pathways controlling the ciliary levels of Shh signal regulators.

Motile and immotile (or primary) cilia are microtubule-based structures that mediate multiple cellular functions, including the transduction of environmental cues, developmental signaling, cellular motility, and modulation of fluid flow. Although their core architectures are similar, motile and primary cilia exhibit marked structural differences that underlie distinct functional properties. However, the extent to which ciliogenesis mechanisms are shared between these different cilia types is not fully described. Here, we report that the atypical MAP kinase MAPK15 (ERK7/8), implicated in the formation of vertebrate motile cilia, also regulates the formation of primary cilia in sensory neurons and human cells. We find that MAPK15 localizes to a basal body subdomain with the ciliopathy protein BBS7 and to cell-cell junctions. MAPK15 also regulates the localization of ciliary proteins involved in cilium structure, transport, and signaling. Our results describe a primary cilia-related role for this poorly studied member of the MAPK family, and indicate a broad requirement for MAPK15 in the formation of multiple ciliary classes across species.