Mutations in Outer Dynein Arm Heavy Chain DNAH9 Cause Motile Cilia Defects and Situs Inversus

Area of Science:

• Cell Biology
• Genetics
• Respiratory Medicine

Background:

• Motile cilia are crucial for clearing airways and moving fluids, driven by dynein motor proteins.
• Mutations in dynein genes cause primary ciliary dyskinesia (PCD), a condition of impaired mucociliary clearance and chronic respiratory disease.
• DNAH9 is a ciliary outer dynein arm (ODA) heavy chain gene.

Purpose of the Study:

• To investigate the role of DNAH9 mutations in primary ciliary dyskinesia (PCD).
• To characterize the structural and functional consequences of DNAH9 mutations in human respiratory cilia.
• To explore the evolutionary conservation and clinical implications of DNAH9 mutations.

Main Methods:

• Next-generation sequencing to identify DNAH9 mutations in PCD patients.
• Analysis of nasal respiratory epithelial cilia from affected individuals.
• 3D electron tomography for ultrastructural examination of cilia.
• Functional studies using Paramecium DNAH9 knockdown.

Main Results:

• DNAH9 mutations were detected in individuals with PCD and situs inversus, and in one case of male infertility.
• Mutations led to a loss of DNAH9/DNAH5-containing type 2 ODAs in the distal region of cilia.
• Affected cilia exhibited reduced beating frequency and subtle pattern defects, impacting distal motility.
• Ultrastructural studies confirmed regional ODA loss or volume reduction in the distal cilium.
• Paramecium knockdown confirmed DNAH9's conserved role in cilia motility and ODA stability.

Conclusions:

• DNAH9 mutations impair cilia function by disrupting distal ODA structure, contributing to the PCD disease spectrum.
• While DNAH9 mutations affect cilia motility, some respiratory mucociliary clearance may be preserved.
• The findings highlight DNAH9 as a significant gene in PCD pathogenesis, particularly affecting upper respiratory tract symptoms.