Abstract
Primary cilia form by two pathways: an extracellular pathway in which the cilium grows out from the cell surface and an intracellular pathway in which the nascent cilium forms inside the cell. Here we identify the GTPase Rab34 as a selective mediator of intracellular ciliogenesis. We find that Rab34 is required for formation of the ciliary vesicle at the mother centriole and that Rab34 marks the ciliary sheath, a unique sub-domain of assembling intracellular cilia. Rab34 activity is modulated by divergent residues within its GTPase domain, and ciliogenesis requires GTP binding and turnover by Rab34. Because Rab34 is found on assembly intermediates that are unique to intracellular ciliogenesis, we tested its role in the extracellular pathway used by MDCK cells. Consistent with Rab34 acting specifically in the intracellular pathway, MDCK cells ciliate independently of Rab34 and paralog Rab36. Together, these findings reveal a new context-specific molecular requirement for ciliary membrane biogenesis.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
Summary Cilia assemble by different pathways in different cell types, but the underlying molecular mechanisms are poorly understood. Here, atypical GTPase Rab34 is found to localize to the ciliary sheath of nascent intracellular cilia and to mediate ciliary membrane formation specifically in the intracellular ciliogenesis pathway.
Abbreviations
- cytoD
- cytochalasin D
- DAV
- Distal appendage vesicle
- FIB-SEM
- Focused ion beam scanning electron microscopy
- GAP
- GTPase activating protein
- GEF
- Guanine nucleotide exchange factor
- Hh
- Hedgehog
- LAP
- Localization and affinity purification tag (containing GFP, TEV protease site, and S-tag)
- Nb
- Nanobody
- GEF
- Guanine nucleotide exchange factor
- polyE-tub
- polyglutamylated tubulin
- sgRNA
- single guide RNA
- SIM
- Structured illumination microscopy