Abstract
Cilia beating is powered by the inner and outer dynein arms (IDAs and ODAs). These multi-subunit macrocomplexes are arranged in two rows on each outer doublet along the entire cilium length, except its distal end. To generate cilia beating, the activity of ODAs and IDAs must be strictly regulated locally by interactions with the dynein arm-associated structures within each ciliary unit and coordinated globally in time and space between doublets and along the axoneme. Here, we provide evidence of a novel ciliary complex composed of two conserved WD-repeat proteins, Fap43p and Fap44p. This complex is adjacent to another WD-repeat protein, Fap57p, and most likely the two-headed inner dynein arm, IDA I1. Loss of either protein results in altered waveform, beat stroke and reduced swimming speed. The ciliary localization of Fap43p and Fap44p is interdependent in the ciliate Tetrahymena thermophila.
Highlights
Cilia and their homologous structures, flagella, are evolutionarily conserved organelles that convert the chemical energy released during ATP hydrolysis into a mechanical force to power cell motility or generate fluid flows at the epithelial cell surface
Our attention was drawn to the Tetrahymena ortholog of Chlamydomonas reinhardtii Fap43p and the human protein Wdr96p (WD-repeat protein 96)
The phylogenetic screen showed that Fap43p/Wdr96p orthologs are present in organisms that assemble motile cilia but not in the worm C. elegans, which forms only immotile sensory cilia (Fig. S1)
Summary
Cilia and their homologous structures, flagella, are evolutionarily conserved organelles that convert the chemical energy released during ATP hydrolysis into a mechanical force to power cell motility or generate fluid flows at the epithelial cell surface. The canonical motile cilium (this term will be used hereafter for both cilia and flagella) consists of a 9 + 2 microtubular core, called the axoneme, and multi-subunit complexes, such as the outer and inner dynein arms (ODAs and IDAs), radial spokes (RSs), the nexin–dynein regulatory complex (N–DRC) and the modifier of inner dynein arms (MIA) complex. The existence of linker structures between outer and inner dynein arms suggests a possible cross-talk between these structures [2, 8, 14]
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