RESUMO
Tubulin glutamylation is a post-translational modification that occurs predominantly in the ciliary axoneme and has been suggested to be important for ciliary function. However, its relationship to disorders of the primary cilium, termed ciliopathies, has not been explored. Here we mapped a new locus for Joubert syndrome (JBTS), which we have designated as JBTS15, and identified causative mutations in CEP41, which encodes a 41-kDa centrosomal protein. We show that CEP41 is localized to the basal body and primary cilia, and regulates ciliary entry of TTLL6, an evolutionarily conserved polyglutamylase enzyme. Depletion of CEP41 causes ciliopathy-related phenotypes in zebrafish and mice and results in glutamylation defects in the ciliary axoneme. Our data identify CEP41 mutations as a cause of JBTS and implicate tubulin post-translational modification in the pathogenesis of human ciliary dysfunction.
Assuntos
Doenças Cerebelares/genética , Cílios/genética , Transtornos da Motilidade Ciliar/genética , Anormalidades do Olho/genética , Ácido Glutâmico/metabolismo , Doenças Renais Policísticas/genética , Proteínas/genética , Tubulina (Proteína)/metabolismo , Animais , Centrossomo/metabolismo , Mapeamento Cromossômico , Cílios/metabolismo , Feminino , Loci Gênicos , Humanos , Masculino , Camundongos , Mutação , Peptídeo Sintases/metabolismo , Polimorfismo de Nucleotídeo Único , Processamento de Proteína Pós-Traducional , SíndromeRESUMO
Degeneration of photoreceptors is a common feature of ciliopathies, owing to the importance of the specialized ciliary structure of these cells. Mutations in AHI1, which encodes a cilium-localized protein, have been shown to cause a form of Joubert syndrome that is highly penetrant for retinal degeneration. We show that Ahi1-null mice fail to form retinal outer segments and have abnormal distribution of opsin throughout their photoreceptors. Apoptotic cell death of photoreceptors occurs rapidly between 2 and 4 weeks of age in these mice and is significantly (P = 0.00175 and 0.00613) delayed by a reduced dosage of opsin. This phenotype also shows dosage-sensitive genetic interactions with Nphp1, another ciliopathy-related gene. Although it is not a primary cause of retinal blindness in humans, we show that an allele of AHI1 is associated with a more than sevenfold increase in relative risk of retinal degeneration within a cohort of individuals with the hereditary kidney disease nephronophthisis. Our data support context-specific roles for AHI1 as a contributor to retinopathy and show that AHI1 may explain a proportion of the variability in retinal phenotypes observed in nephronophthisis.
