A delta-tubulin/epsilon-tubulin/Ted protein complex is required for centriole architecture

Abstract

Centrioles have a unique, conserved architecture formed by three linked "triplet" microtubules arranged in nine-fold symmetry. The mechanisms by which these triplet microtubules are formed are not understood and likely involve the noncanonical tubulins delta-tubulin and epsilon-tubulin. Previously, we found that human cells deficient in delta-tubulin or epsilon-tubulin form abnormal centrioles, characterized by an absence of triplet microtubules, lack of central core protein POC5, and a futile cycle of centriole formation and disintegration (Wang et al., 2017). Here, we show that human cells lacking either of the associated proteins TEDC1 and TEDC2 have these same phenotypes. Using ultrastructure expansion microscopy, we find that mutant centrioles elongate to the same length as control centrioles in G2-phase. These mutants fail to recruit inner scaffold proteins of the central core and have an expanded proximal region. During mitosis, the mutant centrioles elongate further before fragmenting and disintegrating. All four proteins physically interact and TEDC1 and TEDC2 are capable forming a subcomplex in the absence of the tubulins. These results support an AlphaFold Multimer model of the tetramer in which delta-tubulin and epsilon-tubulin are predicted to form a heterodimer. TEDC1 and TEDC2 localize to centrosomes and are mutually dependent on each other and on delta-tubulin and epsilon-tubulin for localization. Our results demonstrate that delta-tubulin, epsilon-tubulin, TEDC1, and TEDC2 function together to promote robust centriole architecture. This work also lays the groundwork for future molecular studies of this complex, providing a basis for determining the mechanisms that underlie the assembly and interplay between the triplet microtubules and inner centriole structure.