Rab34 GTPase mediates ciliary membrane formation in the intracellular ciliogenesis pathway

May 02, 2021

Anil Kumar Ganga (1), Margaret C. Kennedy (1), Mai E. Oguchi (2), Shawn Gray (3), Kendall E. Oliver (1), Tracy A. Knight (1), Enrique M.De La Cruz (3), Yuta Homma (2), Mitsunori Fukuda (2), David K. Breslow (1,4)
Current Biology, 31, May 2021: 2895–2905. DOI: 10.1016/j.cub.2021.04.075


cilia; ciliogenesis; ciliopathy; centriole; GTPase; membrane; ciliary vesicle; Rab


The primary cilium is an essential organizing center for signal transduction, and ciliary defects cause congenital disorders known collectively as ciliopathies. Primary cilia form by two pathways that are employed in a cell-type- and tissue-specific manner: an extracellular pathway in which the cilium grows out from the cell surface and an intracellular pathway in which the nascent cilium first forms inside the cell. After exposure to the external environment, cilia formed via the intracellular pathway may have distinct functional properties, as they often remain recessed within a ciliary pocket. However, the precise mechanism of intracellular ciliogenesis and its relatedness to extracellular ciliogenesis remain poorly understood. Here we show that Rab34, a poorly characterized GTPase recently linked to cilia, is 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 polarized MDCK cells. Consistent with Rab34 acting specifically in the intracellular pathway, MDCK cells ciliate independently of Rab34 and its paralog Rab36. Together, these findings establish that different modes of ciliogenesis have distinct molecular requirements and reveal Rab34 as a new GTPase mediator of ciliary membrane biogenesis.

How Our Software Was Used

Dragonfly was used for the manipulation of data sets.

Author Affiliation

(1) Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, CT 06511, USA.
(1) Laboratory of Membrane Trafficking Mechanisms, Department of Integrative Life Sciences, Graduate School of Life Sciences, Tohoku University, Aobayama, Aoba-ku, Sendai, Miyagi 980-8578, Japan.
(2) Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06511, USA.