Genetic compensation for cilia defects in cep290/NPHP6 mutants by upregulation of cilia-associated small GTPases
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ABSTRACT: Mutations in CEP290, a large multidomain coiled coil protein, are associated with multiple cilia-associated syndromes. Over 130 CEP290 mutations have been linked to a wide spectrum of human ciliopathies, raising the question of how mutations in a single gene cause different disease syndromes. In zebrafish the expressivity of cep290 deficiencies were linked to the type of genetic ablation: acute cep290 morpholino knockdown caused severe cilia-related phenotypes while defects in a Crispr/Cas9 genetic mutant were restricted to photoreceptor defects. Here we show that milder phenotypes in genetic mutants were associated with upregulation of genes encoding the cilia-associated small GTPases arl3, arl13b, and unc119b. Upregulation of UNC119b was also observed in urine-derived renal epithelial cells from human JBTS CEP290 patients. Ectopic expression of arl3, arl13b and unc119b in cep290 morphant zebrafish embryos rescued Kupffer's vesicle cilia and partially rescued photoreceptor outer segment defects. The results suggest that genetic compensation by upregulation of genes involved in a common subcellular process, lipidated protein trafficking to cilia, may be a conserved mechanism contributing to genotype-phenotype variations observed in CEP290 deficiencies.
Project description:ARL13B is a small regulatory GTPase that controls ciliary membrane composition in both motile cilia and non-motile primary cilia. In this study, we investigated the role of ARL13B in the efferent ductules, tubules of the male reproductive tract essential to male fertility in which primary and motile cilia co-exist. We used a genetically engineered mouse model to deleteArl13bin efferent ductule epithelial cells, resulting in compromised primary and motile cilia architecture and functions. This deletion led to disturbances in reabsorptive/secretory processes and triggered an inflammatory response. The observed male reproductive phenotype showed significant variability linked to partial infertility, highlighting the importance of ARL13B in maintaining a proper physiological balance in these small ducts. These results emphasize the dual role of both motile and primary cilia functions in regulating efferent duct homeostasis, offering deeper insights into how cilia related diseases affect the male reproductive system.
Project description:Bialleleic pathogenic variants in LCA5 cause one of the most severe forms of Leber congenital amaurosis, an early-onset retinal disease that results in severe visual impairment. Here, we report the use of gene editing to generate isogenic LCA5 knock-out (LCA5 KO) induced pluripotent stem cells (iPSC) and their differentiation to retinal organoids. The molecular and cellular phenotype of the LCA5 KO retinal organoids was studied in detail and compared to isogenic controls as well as patient-derived retinal organoids. The absence of LCA5 was confirmed in retinal organoids by immunohistochemistry and western blotting. There were no major changes in retinal organoid differentiation or ciliation, however, the localisation of CEP290 and IFT88 was significantly altered in LCA5 KO and patient photoreceptor cilia with extension along the axoneme. The LCA5-deficient organoids also had shorter outer segments and rhodopsin was mislocalised to the outer nuclear layer. We also identified transcriptomic and proteomic changes associated with the loss of LCA5. Importantly, treatment with the small molecules eupatilin, fasudil or a combination of both drugs improved rhodopsin traffic to the outer segment and reduced mislocalisation of rhodopsin in the outer nuclear layer. The treatments also effectively reduced CEP290 and IFT88 accumulation along the cilia. The improvements in cilia-associated protein localisation and traffic were accompanied by significant changes in the transcriptome towards control gene expression levels in many of the differentially expressed genes. In summary, iPSC-derived retinal organoids are a powerful model for investigating the molecular and cellular changes associated with loss of LCA5 function and highlight the therapeutic potential of small molecules to treat retinal ciliopathies.
Project description:Eukaryotic cilia and flagella are essential for cell motility and sensory functions. Their biogenesis and maintenance rely on the intraflagellar transport (IFT). Several cargo adapters have been identified to aid IFT cargo transport, but how ciliary cargos are discharged from IFT remains largely unknown. During our explorations of small GTPases ARL13 and ARL3 in Trypanosoma brucei, we found that ODA16, a known IFT cargo adapter found exclusively in motile cilia, is a specific effector of ARL3. To investigate how TbARL3A and TbARL3C regulate TbODA16, we performed proximity-dependent biotin identification (BioID) and mass spectrometry analyses for TbODA16 in the presence or absence of TbARL3A and TbARL3C.
Project description:Both intraflagellar transport (IFT) and lipidated intraflagellar transport (LIFT) pathways are essential for cilia/flagella biogenesis, motility and sensory functions. In the LIFT pathway, lipidated cargoes are transported into the cilia through the coordinated actions of cargo carrier proteins such as Unc119 or PDE6δ, as well as small GTPases Arl13b and Arl3 in the cilium. Our previous studies revealed a single Arl13b ortholog in the evolutionarily divergent Trypanosoma brucei. TbArl13 catalyses two TbArl3 homologs, TbArl3A and TbArl3C, suggesting the presence of a conserved LIFT pathway in these protozoan parasites. Only a single homolog to the cargo carrier protein Unc119 was identified in T. brucei genome, but its function in lipidated protein transport has not been characterized. In this study, we exploited the proximity-based biotinylation approach to identify binding partners of TbUnc119 using an improved version of biotin ligase BioID2. The BioID2 tag was fused to either the N-terminus (3HA-BioID2-TbUnc119) or the C-terminus (TbUnc119-BioID2-HA) of TbUnc119 and expressed using a cumate-inducible expression system in the procyclic cells of T. brucei. We performed LC-MS/MS on the affinity-purified biotinylated samples followed by evaluation of emPAI score.
Project description:Background: Whereas cilia damage and reduced cilia beat frequency have been implicated as causative of reduced mucociliary clearance in smokers, theoretically mucociliary clearance could also be affected by cilia length. Based on models of mucociliary clearance predicting cilia length must exceed the 6 -7 μm airway surface fluid depth to generate force in the mucus layer, we hypothesized cilia height may be decreased in airway epithelium of normal smokers compared to nonsmokers. Methodology/Principal Findings: Cilia length in normal nonsmokers and smokers was evaluated in aldehyde-fixed, paraffin-embedded endobronchial biopsies, and air-dried and hydrated samples brushed from human airway epithelium via fiberoptic bronchoscopy. In 28 endobronchial biopsies, healthy smoker cilia length was reduced 15% compared to nonsmokers (p<0.05). In 47 air-dried samples of airway epithelial cells, smoker cilia length was reduced 13% compared to nonsmokers (p<0.0001). Analysis of the length of individual, detached cilia in 17 samples, smoker cilia length was reduced 9% compared to nonsmokers (p<0.05). Finally, in 16 fully hydrated, unfixed samples, smoker cilia length was reduced 7% compared to nonsmokers (p<0.05). Conclusions/significance: Models predict that a reduction in cilia length would reduce mucociliary clearance, suggesting that smoking-associated shorter airway epithelial cilia plays a significant role in the pathogenesis of smoking-induced lung disease.
Project description:Cilia are microtubule-based hair-like organelles propelling locomotion and extracellular liquid flow or sensing environmental stimuli. As cilia are diffusion barrier-gated subcellular compartments, their protein components are thought to come from the cell body through intraflagellar transport or diffusion. Here we show that cilia locally synthesize proteins to maintain their ultrastructure and functions. Multicilia of mouse ependymal cells were abundant in ribosomal proteins, translation initiation factors, and RNA, including 18S rRNA and tubulin mRNA. The cilia actively generated nascent peptides, including those of tubulin. FMRP, an RNA-binding component of messenger ribonucleoprotein granules critical for local translation, was concentrated in ciliary central lumen. Its depletion by RNAi impaired ciliary nascent peptide production and induced multicilia degeneration. Expression of exogenous FMRP, but not an isoform tethered to mitochondria, rescued the degeneration defects. Therefore, local translation defects in cilia might contribute to the pathology of ciliopathies and other diseases such as Fragile X syndrome.
Project description:Defects in cilia genes that is critical in cilia formation and function can cause complicated ciliopathy syndromes involving multiple organs and tissues; however, the underlying regulatory mechanisms of cilia gene networks in ciliopathy are largely unknown. Here, we define the genome-wide redistribution of chromatin accessibilities and extensive divergence of cilia genes expression programs happened in ciliopathy. Mechanistically, the distinct ciliopathy-activated accessible regions (CAAs) are characterized to positively regulate robust changes of flanking cilia genes, which are a key transcriptional feature of cilia required for the response to developmental signals. Moreover, the single transcriptional factors, ETS1, can be recruited to CAAs thus prominently reconstructing chromatin accessibility in ciliopathy. CAAs collapse driven by ETS1 suppression subsequently cause defective cilia formation and impaired developmental signal transduction, which eventually develops ciliopathy phenotypes of short fins and pericardium edema in larval fishes. Therefore, our results depicted a dynamic landscape of chromatin accessibility in ciliopathy, and uncover an insightful role of ETS1 in controlling global cilia genes transcriptional program by reprogramming widespread chromatin state.
Project description:As signalling organelles, primary cilia regulate their membrane G protein-coupled receptor (GPCR) content by ectocytosis, a process requiring localised actin dynamics at their tip to alter membrane shape.1,2 Mammalian photoreceptor outer segments comprise an expanse of folded membranes (discs) at the tip of highly-specialised connecting cilia (CC), in which photosensitive GPCRs like rhodopsin are concentrated. In an extraordinary feat of biology, outer segment discs are shed and remade daily.3 Defects in this process, due to genetic mutations, cause retinitis pigmentosa (RP), an untreatable, blinding disease. The mechanism by which photoreceptor cilia generate outer segments is therefore fundamental for vision yet poorly understood. Here, we show the membrane deformation required for outer segment disc genesis is driven by dynamic changes in the actin cytoskeleton in a process akin to ectocytosis. Further, we show RPGR, a leading causal RP gene, regulates activity of actin binding proteins crucial to this process. Disc genesis is compromised in Rpgr mouse models, slowing the actin dynamics required for timely disc formation, leading to aborted membrane shedding as ectosome-like vesicles, photoreceptor death and visual loss. Manipulation of actin dynamics partially rescues the phenotype, suggesting this pathway could be targeted therapeutically. These findings help define how actin-mediated dynamics control outer segment turnover.