Staged maturation converts a probasal body template complex into a nucleation-competent basal plate
In the authors' words
The central pair (CP) of microtubules is essential for flagellar motility, yet the molecular events underpinning its nucleation remain poorly defined. Here, we report a comprehensive screen of flagellar transition zone proteins that identifies new central pair assembly proteins (CPAPs). Using expansion microscopy, we reveal a concentric architecture at the basal plate, with themelin and basalin forming nested punctae with radial symmetry surrounding a central core containing TZP103.8, TZP48 and {gamma}-tubulin. A subset of CPAPs pre-assemble at the probasal body, a precursor structure that has not yet built a flagellum, with themelin functioning as the architectural template and master recruiter, and TZP103.8 and {gamma}-tubulin IFT-dependant addition being the final step of basal plate activation. Strikingly, in the absence of TZP103.8, {gamma}-tubulin still reaches the basal plate but is insufficient for central pair nucleation. We propose the staged assembly of CPAPs progressively constructs a structural template that geometrically constrains {gamma}-tubulin into the positions and orientations required for CP nucleation.
Appeared: Friday, September 25. bioRxiv. Preprint, not yet peer-reviewed.