Cilia or eukaryotic flagella are microtubule-based organelles found across the eukaryotic tree of life. Their very high aspect ratio and crowded interior are unfavorable to diffusive transport of most components required for their assembly and maintenance. Instead, a system of intraflagellar transport (IFT) trains moves cargo rapidly up and down the cilium (Figure 1A).1-3 Anterograde IFT, from the cell body to the ciliary tip, is driven by kinesin-II motors, whereas retrograde IFT is powered by cytoplasmic dynein-1b motors.4 Both motors are associated with long chains of IFT protein complexes, known as IFT trains, and their cargoes.5-8 The conversion from anterograde to retrograde motility at the ciliary tip involves (1) the dissociation of kinesin motors from trains,9 (2) a fundamental restructuring of the train from the anterograde to the retrograde architecture,8,10,11 (3) the unloading and reloading of cargo,2 and (4) the activation of the dynein motors.8,12 A prominent hypothesis is that there is dedicated calcium-dependent protein-based machinery at the ciliary tip to mediate these processes.4,13 However, the mechanisms of IFT turnaround have remained elusive. In this study, we use mechanical and chemical methods to block IFT at intermediate positions along the cilia of the green algae Chlamydomonas reinhardtii, in normal and calcium-depleted conditions. We show that IFT turnaround, kinesin dissociation, and dynein-1b activation can consistently be induced at arbitrary distances from the ciliary tip, with no stationary tip machinery being required. Instead, we demonstrate that the anterograde-to-retrograde conversion is a calcium-independent intrinsic ability of IFT.

• Klíčová slova
• TIRF microscopy, cilia and flagella, ciliary tip, intraflagellar transport, micromanipulator, total-internal reflection microscopy,
• MeSH
• biologický transport MeSH
• cilie metabolismus   MeSH
• cytoplazmatické dyneiny metabolismus   MeSH
• dyneiny * metabolismus   MeSH
• flagella fyziologie   MeSH
• kineziny * MeSH
• vápník metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• cytoplazmatické dyneiny MeSH
• dyneiny * MeSH
• kineziny * MeSH
• vápník MeSH

Cilia assembly and function rely on the bidirectional transport of components between the cell body and ciliary tip via Intraflagellar Transport (IFT) trains. Anterograde and retrograde IFT trains travel along the B- and A-tubules of microtubule doublets, respectively, ensuring smooth traffic flow. However, the mechanism underlying this segregation remains unclear. Here, we test whether tubulin detyrosination (enriched on B-tubules) and tyrosination (enriched on A-tubules) have a role in IFT logistics. We report that knockout of tubulin detyrosinase VashL in Chlamydomonas reinhardtii causes frequent IFT train stoppages and impaired ciliary growth. By reconstituting IFT train motility on de-membranated axonemes and synthetic microtubules, we show that anterograde and retrograde trains preferentially associate with detyrosinated and tyrosinated microtubules, respectively. We propose that tubulin tyrosination/detyrosination is crucial for spatial segregation and collision-free IFT train motion, highlighting the significance of the tubulin code in ciliary transport.

• MeSH
• axonema * metabolismus   MeSH
• biologický transport MeSH
• Chlamydomonas reinhardtii * metabolismus   genetika   MeSH
• cilie metabolismus   MeSH
• flagella * metabolismus   MeSH
• mikrotubuly * metabolismus   MeSH
• tubulin * metabolismus   MeSH
• tyrosin * metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• tubulin * MeSH
• tyrosin * MeSH

Unc-51-like kinase (ULK) family serine-threonine protein kinase homologues have been linked to the function of motile cilia in diverse species. Mutations in Fused/STK36 and ULK4 in mice resulted in hydrocephalus and other phenotypes consistent with ciliary defects. How either protein contributes to the assembly and function of motile cilia is not well understood. Here we studied the phenotypes of ULK4 and Fused gene knockout (KO) mutants in the flagellated protist Leishmania mexicana. Both KO mutants exhibited a variety of structural defects of the flagellum cytoskeleton. Biochemical approaches indicate spatial proximity of these proteins and indicate a direct interaction between the N-terminus of LmxULK4 and LmxFused. Both proteins display a dispersed localization throughout the cell body and flagellum, with enrichment near the flagellar base and tip. The stable expression of LmxULK4 was dependent on the presence of LmxFused. Fused/STK36 was previously shown to localize to mammalian motile cilia, and we demonstrate here that ULK4 also localizes to the motile cilia in mouse ependymal cells. Taken together these data suggest a model where the pseudokinase ULK4 is a positive regulator of the kinase Fused/ STK36 in a pathway required for stable assembly of motile cilia.

• MeSH
• cilie metabolismus   MeSH
• flagella * metabolismus   MeSH
• mikrotubuly metabolismus   MeSH
• myši MeSH
• protein-serin-threoninkinasy * metabolismus   MeSH
• savci metabolismus   MeSH
• zvířata MeSH
• Check Tag
• myši MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• protein-serin-threoninkinasy * MeSH
• Stk36 protein, mouse MeSH Prohlížeč

Skeletal ciliopathies are a heterogeneous group of autosomal recessive osteochondrodysplasias caused by defects in formation, maintenance and function of the primary cilium. Mutations in the underlying genes affect the molecular motors, intraflagellar transport complexes (IFT), or the basal body. The more severe phenotypes are caused by defects of genes of the dynein-2 complex, where mutations in DYNC2H1, WDR34 and WDR60 have been identified. In a patient with a Jeune-like phenotype we performed exome sequencing and identified compound heterozygous missense and nonsense mutations in DYNC2LI1 segregating with the phenotype. DYNC2LI1 is ubiquitously expressed and interacts with DYNC2H1 to form the dynein-2 complex important for retrograde IFT. Using DYNC2LI1 siRNA knockdown in fibroblasts we identified a significantly reduced cilia length proposed to affect cilia function. In addition, depletion of DYNC2LI1 induced altered cilia morphology with broadened ciliary tips and accumulation of IFT-B complex proteins in accordance with retrograde IFT defects. Our results expand the clinical spectrum of ciliopathies caused by defects of the dynein-2 complex.

• MeSH
• cilie metabolismus   MeSH
• cytoplazmatické dyneiny chemie   genetika   MeSH
• exom genetika   MeSH
• fibroblasty metabolismus   MeSH
• fluorescenční protilátková technika MeSH
• heterozygot MeSH
• lidé MeSH
• mutace genetika   MeSH
• nesmyslný kodon genetika   MeSH
• sekvenční analýza DNA MeSH
• terciární struktura proteinů MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• cytoplazmatické dyneiny MeSH
• DYNC2LI1 protein, human MeSH Prohlížeč
• nesmyslný kodon MeSH

The primary cilium, a microtubule-based organelle found in most cells, is a centre for mechano-sensing fluid movement and cellular signalling, notably through the Hedgehog pathway. We recently found that each lens fibre cell has an apically situated primary cilium that is polarised to the side of the cell facing the anterior pole of the lens. The direction of polarity is similar in neighbouring cells so that in the global view, lens fibres exhibit planar cell polarity (PCP) along the equatorial-anterior polar axis. Ciliogenesis has been associated with the establishment of PCP, although the exact relationship between PCP and the role of cilia is still controversial. To test the hypothesis that the primary cilia have a role in coordinating the precise alignment/orientation of the fibre cells, IFT88, a key component of the intraflagellar transport (IFT) complex, was removed specifically from the lens at different developmental stages using several lens-specific Cre-expressing mouse lines (MLR10- and LR-Cre). Irrespective of which Cre-line was adopted, both demonstrated that in IFT88-depleted cells, the ciliary axoneme was absent or substantially shortened, confirming the disruption of primary cilia formation. However no obvious histological defects were detected even when IFT88 was removed from the lens placode as early as E9.5. Specifically, the lens fibres aligned/oriented towards the poles to form the characteristic Y-shaped sutures as normal. Consistent with this, in primary lens epithelial explants prepared from these conditional knockout mouse lenses, the basal bodies still showed polarised localisation at the apical surface of elongating cells upon FGF-induced fibre differentiation. We further investigated the lens phenotype in knockouts of Bardet-Biedl Syndrome (BBS) proteins 4 and 8, the components of the BBSome complex which modulate ciliary function. In these BBS4 and 8 knockout lenses, again we found the pattern of the anterior sutures formed by the apical tips of elongating/migrating fibres were comparable to the control lenses. Taken together, these results indicate that primary cilia do not play an essential role in the precise cellular alignment/orientation of fibre cells. Thus, it appears that in the lens cilia are not required to establish PCP.

• Klíčová slova
• Bardet–Biedl Syndrome (BBS), IFT88, Lens, Planar cell polarity (PCP), Primary cilium,
• MeSH
• cilie fyziologie   MeSH
• cytoskeletální proteiny MeSH
• epitelové buňky ultrastruktura   MeSH
• kultivované buňky MeSH
• myši knockoutované MeSH
• nádorové supresorové proteiny genetika   MeSH
• oční čočka ultrastruktura   MeSH
• polarita buněk MeSH
• proteiny asociované s mikrotubuly genetika   MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Research Support, N.I.H., Extramural MeSH
• Názvy látek
• BBS4 protein, mouse MeSH Prohlížeč
• cytoskeletální proteiny MeSH
• nádorové supresorové proteiny MeSH
• proteiny asociované s mikrotubuly MeSH
• Tg737Rpw protein, mouse MeSH Prohlížeč
• Ttc8 protein, mouse MeSH Prohlížeč