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

Abstract

Cilia have been classified as sensory or motile types on the basis of functional and structural characteristics; however, factors important for regulation of assembly of different cilia types are not well understood. Hepatocyte nuclear factor-3/forkhead homologue 4 (HFH-4) is a winged helix/forkhead transcription factor expressed in ciliated cells of the respiratory tract, oviduct, and ependyma in late development through adulthood. Targeted deletion of the Hfh4 gene resulted in defective ciliogenesis in airway epithelial cells and randomized left-right asymmetry so that half the mice had situs inversus. In HFH-4-null mice, classic motile type cilia with a 9 + 2 microtubule ultrastructure were absent in epithelial cells, including those in the airways. In other organs, sensory cilia with a 9 + 0 microtubule pattern, such as those on olfactory neuroepithelial cells, were present. Ultrastructural analysis of mutant cells with absent 9 + 2 cilia demonstrated that defective ciliogenesis was due to abnormal centriole migration and/or apical membrane docking, suggesting that HFH-4 functions to direct basal body positioning or anchoring. Evaluation of wild-type embryos at gestational days 7.0 to 7.5 revealed Hfh4 expression in embryonic node cells that have monocilium, consistent with a function for this factor at the node in early determination of left- right axis. Analysis of the node of HFH-4 mutant embryos revealed that, in contrast to absent airway cilia, node cilia were present. These observations indicate that there are independent regulatory pathways for node ciliogenesis compared with 9 + 2 type ciliogenesis in airways, and support a central role for HFH-4 in ciliogenesis and left-right axis formation.