The Structure of Cilium Inner Junctions Revealed by Electron Cryo-tomography

Area of Science:

• Cell Biology
• Structural Biology
• Biochemistry

Background:

• Cilia are vital microtubule-based organelles essential for numerous cellular processes.
• Cilium assembly, starting at the basal body and extending to the axoneme, is complex and not fully understood.
• Limited knowledge exists regarding the molecular architecture and assembly mechanisms of cilia.

Purpose of the Study:

• To elucidate the molecular architecture of the cilium's inner junction at subnanometer resolution.
• To identify and map the distribution of basal body and axoneme components.
• To investigate the role of specific proteins in basal body structural integrity and cilium assembly.

Main Methods:

• Electron cryotomography (cryo-ET) was employed to capture high-resolution images.
• Subtomogram averaging was utilized to reconstruct detailed structural models.
• Functional studies involved gene knockout (Poc1) to assess structural consequences.

Main Results:

• Subnanometer resolution structures of the basal body (proximal and central core) and flagellar axoneme inner junctions were obtained.
• Identification of numerous basal body and axoneme protein components.
• Discovery that proteins exhibit region-specific localization, forming localized interaction networks.
• Poc1 knockout destabilized triplet microtubules and led to basal body defects, with axoneme components infiltrating the mutant basal body.

Conclusions:

• The study provides unprecedented molecular insights into cilium assembly at inner junctions.
• Findings highlight the precise spatial regulation of protein distribution and function within cilia.
• The research underscores the importance of specific basal body components for structural stability and proper ciliary formation.