A molecular ruler determines the repeat length in eukaryotic cilia and flagella

Abstract

Existence of cellular structures with specific size raises a fundamental question in biology: How do cells measure length? One conceptual answer to this question is by a molecular ruler, but examples of such rulers in eukaryotes are lacking. In this work, we identified a molecular ruler in eukaryotic cilia and flagella. Using cryo-electron tomography, we found that FAP59 and FAP172 form a 96-nanometer (nm)-long complex in Chlamydomonas flagella and that the absence of the complex disrupted 96-nm repeats of axonemes. Furthermore, lengthening of the FAP59/172 complex by domain duplication resulted in extension of the repeats up to 128 nm, as well as duplication of specific axonemal components. Thus, the FAP59/172 complex is the molecular ruler that determines the 96-nm repeat length and arrangements of components in cilia and flagella.

In Situ Localization of N and C Termini of Subunits of the Flagellar Nexin-Dynein Regulatory Complex (N-DRC) Using SNAP Tag and Cryo-electron Tomography

“…Recently, biotin carboxyl carrier protein that can bind biotin covalently has been used successfully to tag and localize axonemal proteins in Chlamydomonas axonemes using cryo-ET (41)(42)(43). Here, we developed a SNAP tag-based labeling approach for cryo-ET studies.…”

Genetics and biology of primary ciliary dyskinesia

“…For instance, cryoelectron tomography of biochemically pure ciliary and flagellar preparations from these model organisms, have allowed the resolution and localization of individual proteins [29-31]. In addition, the waveform analysis of Chlamydomonas flagella is simplified compared to human cilia.…”

“…Of note, CCDC39 and CCDC40 mutations are almost exclusively null alleles, which indicate that complete absence of protein is required to lead to disease [48]. CCDC39 and CCDC40 have recently been observed to function as a cilia “ruler” to promote the accurate spacing of the radial spokes along the axoneme [31]. These proteins are necessary for construction of the intricate scaffolding mechanism that allows structures of the cilia axoneme to align in a 96-nm repeat pattern along the microtubule doublets.…”

Radial Spokes—A Snapshot of the Motility Regulation, Assembly, and Evolution of Cilia and Flagella

“…This arrangement is consistent with distinct inner dynein anomalies in mia mutants (King and Dutcher 1997) and N-DRC mutants (Piperno et al 1992). These precise structural relationships are predetermined by a complex coined as a molecular ruler that is, surprisingly, comprised of only two coiled-coil paralogous proteins (FAP59 and FAP172) (Oda et al 2014a). Defects in their encoding genes in Chlamydomonas mutants ( pf7 and pf8) result in diminished inner dynein arms and N-DRC.…”