Cells release extracellular vesicles (EVs) that serve as nano-sized packages allowing for exchange of protein and genetic content. Cilia are hair-like projections that play important roles in development and signaling. The cilium both releases and binds to EVs. EVs play a role in cell signaling in health and pathologies, and may carry beneficial or toxic cargo. An understanding of the biogenesis, release, uptake, and signaling of ciliary EVs is lacking. Using C. elegans as a model, we aim to identify the molecules and mechanisms involved in EV biology. A subset of the ciliated neurons of C. elegans release EVs containing cargo that include the polycystins LOV-1 and PKD-2 and a myristoylated protein CIL-7 (Wang et al. Current Biology 2014; Maguire et al. MBoC 2015). Transcriptional profiling of the EV releasing neurons (EVNs) revealed candidates that could play a role in EV biogenesis and/or release (Wang et al. Current Biology 2015).
rab-28 is expressed in all ciliated neurons of C.elegans including the EVNs.
rab-28 encodes a small RAB GTPase. RAB-28 is important for amphid ciliary ultrastructure, amphid glial sheath cell volumes, and amphid-mediated sensory behaviors (Jensen. et al. PLoS Genetics 2016). Here, we explore the role of RAB-28 in EVNs. We investigated the role of RAB-28 in EV biology. We examined shedding and release of GFP-tagged EV cargoes using live imaging of
rab-28(
tm2636) mutants.
rab-28 mutants display altered localization of ciliary EV cargoes PKD-2 and CIL-7. Defects in the release of EV cargo from the tips of EVNs and/or alterations in the ciliary localization of GFP-tagged EV cargo in the EVNs may indicate defects in ciliary trafficking or defects in EV biogenesis and/or release. We are examining ciliary ultrastructure and EVs in
rab-28 mutant males using transmission electron microscopy (TEM). The EV releasing CEM cilia have a unique ciliary ultrastructure and are housed within the cephalic sensillum (Silva et al. Current Biology 2017). The male cephalic sensillum is comprised of CEM and CEP neurons, and glial support and socket cells, the latter create a lumenal space that contains EVs. We are determining whether
rab-28 regulates CEM ciliogenesis, the integrity of the cephalic sensillum, or EV biogenesis. Our work could shed light on the contribution of ciliary ultrastructure and cilia-glia interactions to EV biology.