TTC12 Loss-of-Function Mutations Cause Primary Ciliary Dyskinesia and Unveil Distinct Dynein Assembly Mechanisms in Motile Cilia Versus Flagella

Thomas, Lucie and Bouhouche, Khaled and Whitfield, Marjorie and Thouvenin, Guillaume and Coste, Andre and Louis, Bruno and Szymanski, Claire and Bequignon, Emilie and Papon, Jean-François and Castelli, Manon and Lemullois, Michel and Dhalluin, Xavier and Drouin-Garraud, Valérie and Montantin, Guy and Tissier, Sylvie and Duquesnoy, Philippe and Copin, Bruno and Dastot, Florence and Couvet, Sandrine and Barbotin, Anne-Laure and Faucon, Catherine and Honore, Isabelle and Maitre, Bernard and Beydon, Nicole and Tamalet, Aline and Rives, Nathalie and Koll, France and Escudier, Estelle and Tassin, Anne-Marie and Touré, Aminata and Mitchell, Valérie and Amselem, Serge and Legendre, Marie


Cilia and flagella are evolutionarily conserved organelles whose motility relies on the outer and inner dynein arm complexes (ODAs and IDAs). Defects in ODAs and IDAs result in primary ciliary dyskinesia (PCD), a disease characterized by recurrent airway infections and male infertility. PCD mutations in assembly factors have been shown to cause a combined ODA-IDA defect, affecting both cilia and flagella. We identified four loss-of-function mutations in TTC12, which encodes a cytoplasmic protein, in four independent families in which affected individuals displayed a peculiar PCD phenotype characterized by the absence of ODAs and IDAs in sperm flagella, contrasting with the absence of only IDAs in respiratory cilia. Analyses of both primary cells from individuals carrying TTC12 mutations and human differentiated airway cells invalidated for TTC12 by a CRISPR-Cas9 approach revealed an IDA defect restricted to a subset of single-headed IDAs that are different in flagella and cilia, whereas TTC12 depletion in the ciliate Paramecium tetraurelia recapitulated the sperm phenotype. Overall, our study, which identifies TTC12 as a gene involved in PCD, unveils distinct dynein assembly mechanisms in human motile cilia versus flagella.