The Ciliary Rootlet Maintains Long-Term Stability of Sensory Cilia

Abstract

The striated ciliary rootlet is a prominent cytoskeleton originating from basal bodies of ciliated cells. Although a familiar structure in cell biology, its function has remained unresolved. In this study, we carried out targeted disruption in mice of the gene for rootletin, a component of the rootlet. In the mutant, ciliated cells are devoid of rootlets. Phototransduction and ciliary beating in sensory and motile cilia initially exhibit no apparent functional deficits. However, photoreceptors degenerate over time, and mutant lungs appear prone to pathological changes consistent with insufficient mucociliary clearance. Further analyses revealed a striking fragility at the ciliary base in photoreceptors lacking rootlets. In vitro assays suggest that the rootlet is among the least dynamic of all cytoskeletons and interacts with actin filaments. Thus, a primary function of the rootlet is to provide structural support for the cilium. Inasmuch as photoreceptors elaborate an exceptionally enlarged sensory cilium, they are especially dependent on the rootlet for structural integrity and long-term survival.

ACKNOWLEDGMENTS

We thank Guohua Yue for help in constructing the targeting vector; Norman Michaud and Akella Sreedevi for some histology preparations; O. Bulgakov, D. Hong, E. Mark, M. Sandberg, X. Liu, and Y. Zhao for suggestions; and Shioko Kimura for the Ym1 antibody.

This work was supported by grants from the National Institutes of Health (EY16442, EY11358, EY14104, and EY12950), Philip Morris USA Inc. and Philip Morris International, and the Foundation Fighting Blindness.