The 9 + 2 Axoneme Anchors Multiple Inner Arm Dyneins and a Network of Kinases and Phosphatases That Control Motility

Cilia and flagella are found on a variety of cell types, ranging from single cell protozoa and sperm to the ciliated epithelia of the respiratory and reproductive tracts. Despite this diversity, most motile cilia and flagella contain a highly ordered structure, the 9 + 2 axoneme (Fig. 1 A), which is composed of >250 distinct, but well conserved polypeptides (Luck 1984). Ciliary motility is generated by the dynein-driven sliding of outer doublet microtubules. Defects in the dynein motors or components that regulate their activity can have profound consequences; in vertebrates, these include infertility, respiratory disease, and defects in the determination of the left–right axis during embryonic development (Afzelius 1999; Supp et al. 2000). The biochemical complexity of the organelle has made it challenging to identify the relevant loci by traditional mapping methods (...