The Pcdp1 complex coordinates the activity of dynein isoforms to produce wild-type ciliary motility

Generating the complex waveforms characteristic of beating cilia requires the coordinated activity of multiple dynein isoforms anchored to the axoneme. We previously identified a complex associated with the C1d projection of the central apparatus that includes primary ciliary dyskinesia protein 1 (Pcdp1). Reduced expression of complex members results in severe motility defects, indicating that C1d is essential for wild-type ciliary beating. To define a mechanism for Pcdp1/C1d regulation of motility, we took a functional and structural approach combined with mutants lacking C1d and distinct subsets of dynein arms. Unlike mutants completely lacking the central apparatus, dynein-driven microtubule sliding velocities are wild type in C1d-defective mutants. However, coordination of dynein activity among microtubule doublets is severely disrupted. Remarkably, mutations in either outer or inner dynein arm restore motility to mutants lacking C1d, although waveforms and beat frequency differ depending on which isoform is mutated. These results define a unique role for C1d in coordinating the activity of specific dynein isoforms to control ciliary motility.