Control of axonemal inner dynein arms

This chapter provides an overview of the structure, organization, and regulation of the inner dynein arms, with particular focus on I1 dynein/dynein f. Although there is much evidence from Chlamydomonas for the presence of seven distinct major inner-arm dyneins, their precise arrangement in the axoneme and regulation by second messengers are not completely understood. The fundamental, motile machinery is the 9+2 axoneme, composed of nine outer doublet microtubules and two central singlet microtubules with associated structural projections The axoneme is enclosed by the ciliary membrane, a highly specialized extension of the plasma membrane required for both the regulation of ciliary motility and for sensory functions of the cilium. Studies using diverse, experimental systems have also revealed that second messengers and target signaling proteins, physically built into the 9+2 axoneme, regulate ciliary and flagellar motility. Data indicates that the downstream regulation of the axonemal signaling pathway occurs through localized control of the dynein motors.