Chapter 7 - Chlamydomonas ciliary central apparatus

Abstract

The two motile cilia on each Chlamydomonas cell, like most motile cilia and flagella across eukaryotes, are built on a 9+2 microtubule architecture. Here we focus on the structure and function of the central apparatus (CA) (also called the central pair complex or just the central pair), which consists of two singlet microtubules and an expanding list of over 60 accessory proteins. Major advances in the identification of these accessory proteins, and ultrastructural mapping of their locations within repeating complexes that project from the surface of CA microtubules, are described, and experimental evidence related to dynein regulation by the interaction of radial spokes via specific projections and by the CA as a whole are discussed. We highlight similarities and differences between the CA of Chlamydomonas and other organisms, focusing specifically on the extent of conservation with human cilia and flagella at both the primary sequence level and at the level of phenotypic contributions of CA proteins (or protein complexes) to axonemal motility.