DGK\u03b4 triggers endoplasmic reticulum release of IFT88-containing vesicles destined for the assembly of primary cilia

Jie Ding,Shen Yue,Xin Tong,Lu Xie,Yixing Yao,Steven Y Cheng,Lei Shao,Huaize Liu

doi:10.1038/s41598-017-05680-8

Abstract

The morphogenic factor Sonic hedgehog (Shh) signals through the primary cilium, which relies on intraflagellar transport to maintain its structural integrity and function. However, the process by which protein and lipid cargos are delivered to the primary cilium from their sites of synthesis still remains poorly characterized. Here, we report that diacylglycerol kinase δ (DGKδ), a residential lipid kinase in the endoplasmic reticulum, triggers the release of IFT88-containing vesicles from the ER exit sites (ERES), thereby setting forth their movement to the primary cilium. Encoded by the gene whose mutations originally implicated the primary cilium as the venue of Shh signaling, IFT88 is known to be part of the complex B that drives the anterograde transport within cilia. We show that IFT88 interacts with DGKδ, and is associated with COPII-coated vesicles at the ERES. Using a combination of RNAi silencing and gene knockout strategies, we further show that DGKδ is required for supporting Shh signaling both in vitro and in vivo, demonstrating the physiological significance of this regulation.

Highlights

The Hedgehog morphogenic pathway plays conserved roles in organizing tissue pattern formation and cell fate determination during the development of a diverse array of organisms[1, 2]
We show that IFT88 is associated with COPII-coated vesicles and it interacts with diacylglycerol kinase δ (DGKδ) at the endoplasmic reticulum (ER) exit site (ERES)
Characterization of flexo/Polaris/Tg737 mutants led to the first insight of the primary cilium as the venue of Sonic hedgehog (Shh) signaling over a decade ago[3], the precise function of IFT88 was still not clear

Summary

Introduction

The Hedgehog morphogenic pathway plays conserved roles in organizing tissue pattern formation and cell fate determination during the development of a diverse array of organisms[1, 2]. Other cytosolic components of the pathway, including downstream transcriptional factors Gli[1, 2, 3] and Gli-binding protein, Suppressor of fused (Sufu), traverse into the primary cilium upon ligand induction[10,11,12] Trafficking of these diverse types of proteins is orchestrated by intraflagellar transport (IFT) complexes and motor proteins[13, 14]; its precise mechanism remains to be determined. The kinase activity of DGKδ is required for triggering the release of IFT88-containing COPII vesicles, thereby setting forth their movement toward the primary cilium This process is essential to the structural and functional integrity of the primary cilium, Shh signaling

Methods

Results

Conclusion