Ciliogenesis and left-right axis defects in forkhead factor HFH-4-null mice

Area of Science:

• Cell Biology
• Developmental Biology
• Genetics

Background:

• Cilia are classified as sensory or motile, but regulatory factors for their assembly are poorly understood.
• Hepatocyte nuclear factor-3/forkhead homologue 4 (HFH-4) is a transcription factor found in ciliated cells.
• HFH-4's role in ciliogenesis and axis determination requires further investigation.

Purpose of the Study:

• To investigate the function of HFH-4 in the regulation of ciliogenesis and left-right axis formation.
• To determine the specific defects in cilia assembly caused by the absence of HFH-4.
• To explore the differential regulation of cilia in various cell types and developmental stages.

Main Methods:

• Gene targeting to create HFH-4-null mice.
• Transmission electron microscopy to analyze cilia ultrastructure.
• Analysis of embryonic development and organ asymmetry.

Main Results:

• HFH-4 deletion resulted in absent 9+2 motile cilia in airway epithelial cells and randomized left-right asymmetry (situs inversus).
• Sensory 9+0 cilia, like those in olfactory neurons, were present in HFH-4-null mice.
• Ultrastructural analysis revealed defects in centriole migration and apical membrane docking in mutant cells.
• HFH-4 is expressed in embryonic node monocilia, but node cilia were present in mutant embryos, suggesting independent regulation.

Conclusions:

• HFH-4 plays a critical role in the ciliogenesis of motile 9+2 cilia, particularly in airway epithelia.
• HFH-4 is essential for establishing left-right axis determination.
• Defective ciliogenesis in HFH-4-null mice is linked to abnormal basal body positioning.
• Distinct regulatory pathways govern node ciliogenesis versus airway 9+2 type ciliogenesis.