Ciliary Rab28 and the BBSome negatively regulate extracellular vesicle shedding.

Breandan N Kennedy,Ken Nguyen,Malan Silva,Fatima Rizvi,David H Hall,Oliver E Blacque,Maureen M Barr,Sofia Tsiropoulou,Stephen P Carter,Ailis L Moran,Jyothi S Akella

doi:10.7554/elife.50580

Abstract

Cilia both receive and send information, the latter in the form of extracellular vesicles (EVs). EVs are nano-communication devices that influence cell, tissue, and organism behavior. Mechanisms driving ciliary EV biogenesis are almost entirely unknown. Here, we show that the ciliary G-protein Rab28, associated with human autosomal recessive cone-rod dystrophy, negatively regulates EV levels in the sensory organs of Caenorhabditis elegans in a cilia specific manner. Sequential targeting of lipidated Rab28 to periciliary and ciliary membranes is highly dependent on the BBSome and the prenyl-binding protein phosphodiesterase 6 subunit delta (PDE6D), respectively, and BBSome loss causes excessive and ectopic EV production. We also find that EV defective mutants display abnormalities in sensory compartment morphogenesis. Together, these findings reveal that Rab28 and the BBSome are key in vivo regulators of EV production at the periciliary membrane and suggest that EVs may mediate signaling between cilia and glia to shape sensory organ compartments. Our data also suggest that defects in the biogenesis of cilia-related EVs may contribute to human ciliopathies.

Highlights

Cilia are conserved microtubule (MT)-based organelles that extend from the surfaces of most eukaryotic cell types
In amphid and phasmid neurons, we previously showed that the Intraflagellar transport (IFT) motility and periciliary membrane (PCM) targeting of GFP-tagged RAB-28Q95L, a putative GTP-preferring and active form of the G-protein, is dependent on the BBSome component bbs-8 (Jensen et al, 2016)
We found that GFP-RAB-28Q95L mislocalization in the amphid and phasmid cilia of bbs-5(gk507) worms is indistinguishable from bbs-8(nx77) mutants; GFP signals are diffused throughout the neurons, with no detectable PCM enrichment or IFT movement (Figure 1, enhanced contrast images and expressivity shown in Figure 1—figure supplement 1A and C)

Summary

Introduction

Cilia are conserved microtubule (MT)-based organelles that extend from the surfaces of most eukaryotic cell types. Defects in primary cilia lead to monosymptomatic and syndromic human disorders, collectively termed ciliopathies These include diseases such as autosomal dominant polycystic kidney disease (ADPKD), retinitis pigmentosa, cone-rod dystrophy and Bardet-Biedl syndrome (BBS) (Waters and Beales, 2011). Intraflagellar transport (IFT) is driven by kinesin-II anterograde (ciliary base to tip) and cytoplasmic dynein 2 retrograde (ciliary tip to base) motors (Rosenbaum and Witman, 2002). Cargo adapters such as the IFT-A/B complexes and the BBSome enable IFT to transport structural and signaling proteins into and out of cilia (Liem et al, 2012; Bhogaraju et al, 2013; Lechtreck, 2015; Nachury, 2018).

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