Heme-binding protein CYB5D1 is a radial spoke component required for coordinated ciliary beating

Area of Science:

• Cell Biology
• Biochemistry
• Molecular Biology

Background:

• Coordinated beating of multiple cilia is essential for various biological processes.
• The molecular mechanisms underlying ciliary coordination remain incompletely understood.

Purpose of the Study:

• To investigate the function of the conserved ciliary protein CYB5D1 in regulating coordinated ciliary beating.
• To elucidate the molecular mechanism by which CYB5D1 influences ciliary function.

Main Methods:

• Characterization of CYB5D1 in zebrafish and Chlamydomonas reinhardtii models.
• Genetic manipulation (mutation and knockdown) to assess CYB5D1 function.
• Biochemical analyses to determine protein interactions and heme-binding properties.
• Assessment of ciliary beating patterns and cellular responses (e.g., phototaxis).

Main Results:

• Mutation or knockdown of CYB5D1 in zebrafish impaired coordinated ciliary beating in the otic vesicle and olfactory epithelium.
• A Chlamydomonas CYB5D1 ortholog mutant exhibited uncoordinated flagellar beating due to a defect in the cis-flagellum.
• CrCYB5D1 was identified as a radial spoke stalk protein that binds heme under oxidizing conditions.
• Loss of CrCYB5D1 led to a reductive shift in flagellar redox state and impaired phototaxis.
• Oxidant treatment restored coordinated flagellar beating in the Crcyb5d1 mutant.

Conclusions:

• CYB5D1 is a crucial protein for maintaining coordinated ciliary beating.
• CYB5D1 integrates environmental and intraciliary signals to regulate ciliary redox state.
• The redox regulation by CYB5D1 is essential for the coordinated function of multiple cilia.