Microtubular protofilaments and subunits of the outer dynein arm in cilia from dogs with primary ciliary dyskinesia.

Using a procedure of membrane solubilization followed by tannic acid fixation-staining, we found abnormally constructed central and B microtubules in cilia from dogs with primary ciliary dyskinesia. We also found that a ciliary abnormality commonly associated with primary ciliary dyskinesia, "shortened outer dynein arms," actually represents the absence of a specific set of the 3 peripheral subunits that make up the outer dynein arms. We believe that this is the first time that these have been reported. Because the proximal subunits of the outer dynein arm are present and attached to the A microtubule, we argue that in these patients there is no structural abnormality of the A microtubule or the A-tubule attachment sites for outer and inner arms and radial spokes. Also, because a majority of cilia in these patients were motile, we believe that the data from this study support the concept that the outer dynein arms are not required for some motion but probably required for normal motility; however, the central microtubules, central microtubular complex, and probably the B tubules are essential for motility.