Arl13b and the exocyst interact synergistically in ciliogenesis

Abstract

Arl13b belongs to the ADP-ribosylation factor family within the Ras superfamily of regulatory GTPases. Mutations in Arl13b cause Joubert syndrome, which is characterized by congenital cerebellar ataxia, hypotonia, oculomotor apraxia, and mental retardation. Arl13b is highly enriched in cilia and is required for ciliogenesis in multiple organs. Nevertheless, the precise role of Arl13b remains elusive. Here we report that the exocyst subunits Sec8, Exo70, and Sec5 bind preferentially to the GTP-bound form of Arl13b, consistent with the exocyst being an effector of Arl13b. Moreover, we show that Arl13b binds directly to Sec8 and Sec5. In zebrafish, depletion of arl13b or the exocyst subunit sec10 causes phenotypes characteristic of defective cilia, such as curly tail up, edema, and abnormal pronephric kidney development. We explored this further and found a synergistic genetic interaction between arl13b and sec10 morphants in cilia-dependent phenotypes. Through conditional deletion of Arl13b or Sec10 in mice, we found kidney cysts and decreased ciliogenesis in cells surrounding the cysts. Moreover, we observed a decrease in Arl13b expression in the kidneys from Sec10 conditional knockout mice. Taken together, our results indicate that Arl13b and the exocyst function together in the same pathway leading to functional cilia.

Multiciliated Cells in Animals

“…This suggests that the PCP pathway controls the recruitment of Sec8-positive vesicles to the BBs to allow BB docking and ciliary membrane extension (Park et al 2008). In agreement with this, the exocyst is required for primary ciliogenesis (Feng et al 2012;Seixas et al 2016). In mouse airway MCCs, ciliary vesicle docking further requires the BB component Chibby, which binds to CEP164 to promote the recruitment of Rabin8 and Rab8 (Burke et al 2014).…”

Role for the IFT-A Complex in Selective Transport to the Primary Cilium

“…Our data indicate that CytoD promotes cilium entry of several membrane and vesicle proteins, although it is currently unclear whether and how these proteins partition with PPC components. A recent study suggested that Arl13b interacts with an exocyst component, Sec5, which localizes to both cilia and the periciliary region in MDCK cells (Seixas et al, 2015). Nonetheless, Sec5 was not found in all Arl13b-positive cilia of RPE1 and NIH-3T3 cells (Seixas et al, 2015), suggesting that membrane transport could differ across cell types.…”

“…A recent study suggested that Arl13b interacts with an exocyst component, Sec5, which localizes to both cilia and the periciliary region in MDCK cells (Seixas et al, 2015). Nonetheless, Sec5 was not found in all Arl13b-positive cilia of RPE1 and NIH-3T3 cells (Seixas et al, 2015), suggesting that membrane transport could differ across cell types. Arl13b was found to co-localize and interact with actin in our study and in HeLa cells (Barral et al, 2012), and here we also show that actin de-polymerization leads to both conversion of Arl13b-actin bundles to dissociated Arl13b-actin nodes and enhanced targeting of Arl13b to centrosome and cilia.…”

Diverse Functions and Signal Transduction of the Exocyst Complex in Tumor Cells

“…Arl13b is one of Arf family member which is associated with the primary cilium (Li et al, ). The conditional deletion of Sec10 in mouse kidneys decreases Arl13b expression and leads to kidney cysts and decreased ciliogenesis in kidney tubule epithelia (Seixas et al, ).…”