Ciliopathies are a group of disorders that arise from ciliary dysfunction. Meckelin (MKS3 or TMEM67) is a conserved transmembrane protein found at the transition zone of ciliated cells. In humans MKS3 is one of 3 genes linked to the ciliopathy Meckel Syndrome. This disease is characterized by occipital meningioencephalocoele, polycystic kidneys, fibrotic changes to the liver, postnatal polydactyly and situs inversus. Paramecium tetraurelia is a single celled ciliated eukaryote. Its surface is organized of a meshwork of cortical units that run the length of the cell. At the center of the cortical units are either one or two basal bodies. In two basal body units only the posterior basal body is ciliated. From the ciliated basal body, three rootlets project in stereotypical orientations: the post-ciliary rootlet projects posteriorly, the transverse microtubule projects toward the adjacent basal body row and the striated rootlet projects anteriorly. Both the post-ciliary rootlet and transverse microtubule are microtubule-based structures. The striated rootlet is composed of multiple subunits that are predicted to have conserved segmented coiled coil domains known as SF-Assemblin domains. In Picariello at al., 2014, we showed that MKS3 is present in the transition zone of Paramecium tetraurelia and that RNAi for MKS3 leads to global ciliary loss. Additionally, RNAi for MKS3 results in the disorganization of the basal body rows. Within the areas of disorganization, the basal bodies along with their striated rootlets, post-ciliary rootlets and transverse microtubules are rotated away from their expected orientation. Interestingly, the post-ciliary rootlet and transverse microtubule are still attached at the expected angles relative to each other within the areas of disorganization. Initial GST pull-down experiments using the coiled coil domain of MKS3 suggest a potential interaction between MKS3 and the striated rootlet family members KdC1 and KdB2. To test potential interactions between MKS3 and the striated rootlet we identified 27 potential striated rootlet family members in Paramecium. Full-length sequences for 13 of these genes were marked at their N-terminus with a 3x FLAG sequence. Components with a conserved SF-Assemblin domain were distributed uniformly within the striated rootlet. Components lacking the SF-Assemblin domain were found in various cellular locations, but not within the striated rootlet. GST pull-down experiments utilizing the MKS3 C-terminus as bait were performed using cells expressing the FLAG-tagged striated rootlet family members. Unfortunately a clear interaction between MKS3 and the striated rootlet remains elusive. The organized nature of the surface of Paramecium has allowed us to identify a previously unrealized function for MKS3. Our immunofluorescence data suggest that MKS3 functions outside the transition zone to maintain basal body row organization by potentially contributing to a link between the basal body and the striated rootlet. Without the link, the migrating basal bodies are free to rotate and project their rootlets in the wrong directions. Although the nature of the link remains elusive, the identification of disorganized basal body rows upon MKS3 reduction suggests that, in addition to ciliary dysfunction, basal body polarity defects may contribute to the development of MKS.

Les cils et flagelles sont des organites cellulaires retrouvés des protozoaires aux mammifères. Une dérégulation de l’assemblage (ciliogenèse) ou de la fonction des cils, entraîne diverses maladies chez l’homme. Parmi les acteurs de la ciliogenèse, se trouvent les facteurs de transcription RFX. La recherche de gènes cibles de RFX chez la drosophile a permis d’identifier le gène Chibby (Cby), précédemment décrit comme un antagoniste de la voie de signalisation Wnt/wingless. Contrairement aux vertébrés, chez les invertébrés aucun lien n’est encore établi entre cil et voie wg. L’identification de cby comme cible de dRFX chez la drosophile suggère une fonction ciliaire de cby et permettrait l’établissement du lien cil/voie wg. CBY se localise à la zone de transition des cils des neurones sensoriels du système nerveux périphérique et aux centrioles des spermatides. Les drosophiles invalidées pour cby présentent un phénotype de non coordination, mais aucun phénotype de type wg. Ces mutants ont des défauts des cils sensoriels, ainsi que des défauts d’organisation des spermatides. De plus, chez les embryons, les protéines actrices du transport intra-flagellaire, NompB et CG11356, sont mal distribuées lorsque CBY est absente. Enfin, chez les mutants, la localisation de la protéine UNC est affectée dans les cellules germinales en fin de spermatogenèse. En conclusion, chez la drosophile, CBY est impliquée dans le tri protéique organisé à la base du cil de neurones sensoriels, de concert avec les autres protéines localisées à la zone de transition. Dans le testicule, CBY est nécessaire à la maturation des spermatides. En revanche, CBY n‟intervient pas dans la régulation de la voie wg / Cilia and flagella are organelles found from protozoa to mammals. Deregulation of the assembly (ciliogenesis) or function of cilia, causes various diseases in humans. Among those involved in ciliogenesis are the RFX transcription factors. The search for RFX target genes in Drosophila identified the Chibby (CBY) gene, previously described as an antagonist of the Wnt / wingless pathway. Unlike in vertebrates, in invertebrates is still no link established between cilia and the wg pathway. The identification of CBY as a target of dRFX in Drosophila suggests a ciliary function of CBY and would allow the establishment of the link cilia / wg pathway. CBY is localized at the transition zone of cilia of sensory neurons of the peripheral nervous system and at centrioles in spermatids. Drosophila invalidated for CBY present a phenotype of uncoordination, but no wg phenotype. These mutants have defects in sensory cilia and defects in organization of spermatids. In addition, in embryos, the distribution of proteins involved in intra-flagellar transport, NompB and CG11356, is affected when CBY is absent. Finally, in the mutants, the localization of the UNC protein is affected in germ cells at the end of spermatogenesis. In conclusion, in Drosophila, CBY is involved in the protein sorting organized at the base of cilia of sensory neurons, with the other proteins located at the transition zone. In the testes, CBY is necessary for the maturation of spermatids. However, CBY is not involved in the regulation of the wg pathway