Research

Cilia-Cilia Joining

A remarkable but poorly understood phenomenon occurs in certain C. elegans sensory neurons: adjacent cilia physically join tip-to-tip, forming elongated inter-ciliary bridges. This cilia-cilia joining process — also called juxtaposed cilia-cilia elongation — represents a novel mode of ciliary remodelling whose molecular basis and physiological significance have remained almost entirely unexplored. The Kaplan Lab is one of the few groups in the world dedicated to understanding this phenomenon.

What is cilia-cilia joining?

In the amphid sensory organ of C. elegans, cilia from neighbouring neurons come into contact and undergo a regulated elongation process in which the membranes of two adjacent cilia fuse or tightly associate. The resulting structure extends beyond the normal cilia length and requires an intact BBSome and specific regulatory GTPases. Disruption of joining correlates with sensory deficits, suggesting a functional role in inter-neuronal communication or sensory integration.

Key findings

ARL13B regulates joining via BBSome

The Joubert syndrome GTPase ARL13B (ARL-13 in C. elegans) regulates juxtaposed cilia-cilia elongation in a BBSome-dependent manner. Loss of ARL-13 or BBS components abolishes joining, linking this process directly to the same molecular machinery disrupted in BBS and JBTS patients. Turan et al., iScience 2025 →

Ultrastructural characterisation

The lab is applying FIB-SEM (focused ion beam scanning electron microscopy) to generate quantitative ultrastructural data on joining sites — resolving membrane topology, inter-ciliary contact geometry, and the organisation of cytoskeletal elements at the junction at nanometre resolution.

IFT dynamics at junction sites

Live TIRF imaging of IFT-B and IFT-A reporters reveals that anterograde and retrograde IFT trains enter and traverse the joined region, suggesting that the joined cilium is not a passive structure but a dynamically maintained compartment with its own transport kinetics. Turan et al., STAR Protoc 2022 →

Open questions

The lab is actively investigating: (1) which membrane fusion or tethering factors mediate the initial contact between cilia; (2) whether joining is regulated by neuronal activity or environmental cues; (3) whether analogous structures exist in vertebrate sensory organs; and (4) whether mutations in joining-related genes contribute to undiagnosed ciliopathy phenotypes in human patients.

Methods

TIRF live imaging FIB-SEM ultrastructure IFT speed & frequency analysis Fluorescent membrane reporters CRISPR/Cas9 knock-out C. elegans sensory assays

Juxtaposed cilia-cilia elongation in C. elegans sensory neurons.

IFT train dynamics imaged by TIRF microscopy. Turan et al., STAR Protoc 2022.

Key publications

Turan et al. 2025 — iScience Turan et al. 2022 — STAR Protoc