The Regulation of Axonemal Bending

This chapter primarily focuses on the regulatory mechanisms, signaling molecules, and the discovery and structural organization of axonemal components, revealed in studies of Chlamydomonas, which control axonemal bending. It also reviews the use of cryoelectron microscopy for elucidating details of axonemal structure, with particular emphasis on how structural components of the axoneme may contribute to control of flagellar motility. The mechanisms are complex and are only just beginning to be understood, but include a physically integrated network of axonemal structures and signaling proteins required for regulation of the dynein motors. This chapter describes the dyneins, radial spokes, and central pair apparatus. Based on diverse studies in Chlamydomonas, modulation of axonemal bending involves the central pair apparatus, the radial spokes, and the structures including the DRC and the axonemal kinases and phosphatases. The DRC and signaling proteins are thought to regulate dynein-driven microtubule sliding by coupling the central pair apparatus/radial spoke mechanism to the local control of dynein activity.