Feng Zhou1 and Sudipto Roy1,2,3
1 Institute of Molecular and Cell Biology, Proteos, Singapore 138673
2 Department of Biological Sciences, National University of Singapore, Singapore 117543
3 Department of Pediatrics, National University of Singapore, Singapore 119228
Published in Cell; Jul 2, 2015
Motile cilia are hair-like organelles that protrude from the cell surface and are conserved throughout eukaryotes. Motile cilia beat rhythmically, and function in cellular and organismal locomotion and in driving fluid transport over epithelia. In vertebrates, their roles are varied and their dysfunction in humans is associated with disease.
Figure legend: Differentiation of Mono-Motile Cilia
The axoneme, the core of a motile cilium, is built from nine outer doublet microtubules together with a central pair of microtubule singlets. It is seeded by the basal body, a derivative of the mother centriole that associates with the apical cell membrane at the onset of ciliogenesis. Molecular complexes that impart or regulate motility such as the outer and inner dynein arms (ODA and IDA), radial spokes, and the nexin links are attached to the outer doublets and the central pair at regular intervals along the length of the axoneme. Assembly and disassembly of axonemal and motility components is regulated by intraflagellar transport (IFT), with anterograde transport driven by the kinesin-2 motor and retrograde transport facilitated by the cytoplasmic dynein-2 complex. Motility components, such as the dynein arms, are partially assembled with the help of specific assembly factors (DNAAFs) in the cytoplasm before being trafficked into the cilium by IFT. In addition, dedicated docking proteins function as sites for anchoring the motility proteins along the axoneme.
Transcriptional control of motile ciliogenesis is mediated by members of the regulatory factor X (RFX) and the forkhead box J1 (FoxJ1) family proteins. FoxJ1 is the central transcription factor in motile ciliogenesis, and it is essential, and in many instances sufficient, to program cells to differentiate motile cilia. Expression of FoxJ1 occurs in tissues harboring motile cilia, and it activates the expression of a cohort of genes required for motile cilia differentiation and function. The RFX proteins typically control expression of genes that have functions in all types of cilia, such as those for IFT factors. There is cross talk between FoxJ1 and the RFX proteins that facilitates the unique transcriptional programs specifying the distinct identities of different kinds of motile cilia.
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