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Ciliopathies are a group of human disorders caused by dysfunction of primary cilia, ubiquitous microtubule-based organelles involved in transduction of extra-cellular signals to the cell. This function requires the concentration of receptors and channels in the ciliary membrane, which is achieved by complex trafficking mechanisms, in part controlled by the small GTPase RAB8, and by sorting at the transition zone located at the entrance of the ciliary compartment. Mutations in the transition zone gene CC2D2A cause the related Joubert and Meckel syndromes, two typical ciliopathies characterized by central nervous system malformations, and result in loss of ciliary localization of multiple proteins in various models. The precise mechanisms by which CC2D2A and other transition zone proteins control protein entrance into the cilium and how they are linked to vesicular trafficking of incoming cargo remain largely unknown. In this work, we identify the centrosomal protein NINL as a physical interaction partner of CC2D2A. NINL partially co-localizes with CC2D2A at the base of cilia and ninl knockdown in zebrafish leads to photoreceptor outer segment loss, mislocalization of opsins and vesicle accumulation, similar to cc2d2a-/- phenotypes. Moreover, partial ninl knockdown in cc2d2a-/- embryos enhances the retinal phenotype of the mutants, indicating a genetic interaction in vivo, for which an illustration is found in patients from a Joubert Syndrome cohort. Similar to zebrafish cc2d2a mutants, ninl morphants display altered Rab8a localization. Further exploration of the NINL-associated interactome identifies MICAL3, a protein known to interact with Rab8 and to play an important role in vesicle docking and fusion. Together, these data support a model where CC2D2A associates with NINL to provide a docking point for cilia-directed cargo vesicles, suggesting a mechanism by which transition zone proteins can control the protein content of the ciliary compartment., Author Summary Ciliopathies are a group of disorders caused by dysfunction of primary cilia, ubiquitous organelles involved in signal transduction. Mutations in CC2D2A cause two ciliopathies, Joubert and Meckel syndromes, and result in loss of ciliary protein localization. The mechanism by which CC2D2A, located at the ciliary transition zone, controls ciliary protein composition and its link to vesicular trafficking of incoming cargo remain largely unknown. Here, we identify a series of physical interactions linking CC2D2A to vesicular trafficking controlled by the small GTPase RAB8, suggesting a new model, whereby CC2D2A provides a specific docking point for ciliary-bound vesicles at the entrance to the ciliary compartment. We first identify NINL as a physical and genetic interaction partner of CC2D2A, show that both proteins co-localize at the entrance to the cilium and demonstrate that absence of Ninl or Cc2d2a result in similar retinal phenotypes in zebrafish, including mislocalization of Rab8. We further identify MICAL3, a protein known to bind RAB8, as another NINL interaction partner, thus linking CC2D2A to RAB8A-controlled trafficking. Finally, we describe an individual with Joubert syndrome, in whom combined CC2D2A and NINL mutations result in an enhanced phenotype, illustrating the impact of the detected interaction on the disease.