Ciliopathies: The Trafficking Connection

• Published in: Traffic (Copenhagen, Denmark) Denmark), 2014-10, Vol.15 (10), p.1031-1056
• Main Authors: Madhivanan, Kayalvizhi, Aguilar, Ruben Claudio
• Format: Article
• Language: English
• Subjects: Animals; Cilia - metabolism; Cilia - pathology; Ciliary Motility Disorders - genetics; Ciliary Motility Disorders - metabolism; ciliopathies; endocytic pathway; Humans; Mutation; Polycystic Kidney Diseases - genetics; Polycystic Kidney Diseases - metabolism; primary cilia; Protein Transport; secretory pathway; vesicle trafficking
• ISSN: 1398-9219; 1600-0854
• DOI: 10.1111/tra.12195

The primary cilium (PC) is a very dynamic hair‐like membrane structure that assembles/disassembles in a cell‐cycle‐dependent manner and is present in almost every cell type. Despite being continuous with the plasma membrane, a diffusion barrier located at the ciliary base confers the PC properties of a separate organelle with very specific characteristics and membrane composition. Therefore, vesicle trafficking is the major process by which components are acquired for cilium formation and maintenance. In fact, a system of specific sorting signals controls the right of cargo admission into the cilia. Disruption to the ciliary structure or its function leads to multiorgan diseases known as ciliopathies. These illnesses arise from a spectrum of mutations in any of the more than 50 loci linked to these conditions. Therefore, it is not surprising that symptom variability (specific manifestations and severity) among and within ciliopathies appears to be an emerging characteristic. Nevertheless, one can speculate that mutations occurring in genes whose products contribute to the overall vesicle trafficking to the PC (i.e. affecting cilia assembly) will lead to more severe symptoms, whereas those involved in the transport of specific cargoes will result in milder phenotypes. In this review, we summarize the trafficking mechanisms to the cilia and also provide a description of the trafficking defects observed in some ciliopathies which can be correlated to the severity of the pathology. The receptor‐rich, signaling organelle known as primary cilium (PC) has been implicated in a multitude of diseases collectively denominated as ciliopathies. The presence of a defined barrier at its base makes the PC an isolated compartment that needs vesicle trafficking for maintenance and function. This review discusses the major players involved in trafficking to the PC and highlights evidence correlating the severity of the ciliopathy to the trafficking defect involved. Specifically, mild and severe symptoms arise from specific ciliary receptor mislocalization and generalized ciliogenesis defect, respectively.