IFT52 plays an essential role in sensory cilia formation and neuronal sensory function in Drosophila

The emerging functions of intraflagellar transport 52 in ciliary transport and ciliopathies

Ciliary transport in eukaryotic cells is an intricate and conserved process involving the coordinated assembly and functioning of a multiprotein intraflagellar transport (IFT) complex. Among the various IFT proteins, intraflagellar transport 52 (IFT52) plays a crucial role in ciliary transport and is implicated in various ciliopathies. IFT52 is a core component of the IFT-B complex that facilitates movement of cargoes along the ciliary axoneme. Stable binding of the IFT-B1 and IFT-B2 subcomplexes by IFT52 in the IFT-B complex regulates recycling of ciliary components and maintenance of ciliary functions such as signal transduction and molecular movement. Mutations in the IFT52 gene can disrupt ciliary trafficking, resulting in dysfunctional cilia and affecting cellular processes in ciliopathies. Such ciliopathies caused by IFT52 mutations exhibit a wide range of clinical features, including skeletal developmental abnormalities, retinal degeneration, respiratory failure and neurological abnormalities in affected individuals. Therefore, IFT52 serves as a promising biomarker for the diagnosis of various ciliopathies, including short-rib thoracic dysplasia 16 with or without polydactyly. Here, we provide an overview of the IFT52-mediated molecular mechanisms underlying ciliary transport and describe the IFT52 mutations that cause different disorders associated with cilia dysfunction.

A direct interaction between CENTLEIN and RABIN8 is required for primary cilium formation

Primary cilia are formed in nearly all growth-arrested cells and are essential for mammalian development and tissue homeostasis. Defects in primary cilia result in a range of disorders in humans, named ciliopathies. The spatiotemporal localization of RABIN8 on the pericentrosome is an early step in ciliogenesis. Here, we show that CENTLEIN depletion causes the persistent accumulation of RABIN8 on the pericentrosome and primary cilium loss in hTERT-immortalized retinal pigment epithelial cells and murine embryonic fibroblasts. CENTLEIN interacts with RABIN8 directly. A stretch of a 31-amino acid sequence located in the 200‒230 region of the RABIN8 GEF domain is responsible for its physical interaction with CENTLEIN, while expression of the full-length but not the internal deletion lacking the RABIN8-binding site of CENTLEIN largely rescues the ciliogenesis defect provoked by CENTLEIN depletion. Expression of activated RAB8A partially reverses cilium loss in CENTLEIN-null RPE1 cells, so the functional importance of the CENTLEIN-RABIN8 interaction is defined.