PACRG and FAP20 form the inner junction of axonemal doublet microtubules and regulate ciliary motility

Erin E. Dymek, Jianfeng Lin, Gang Fu, Mary E. Porter, Daniela Nicastro, Elizabeth F. Smith

Research output: Contribution to journalArticlepeer-review

17 Scopus citations


We previously demonstrated that PACRG plays a role in regulating dynein-driven microtubule sliding in motile cilia. To expand our understanding of the role of PACRG in ciliary assembly and motility, we used a combination of functional and structural studies, including newly identified Chlamydomonas pacrg mutants. Using cryo-electron tomography we show that PACRG and FAP20 form the inner junction between the A- and B-tubule along the length of all nine ciliary doublet microtubules. The lack of PACRG and FAP20 also results in reduced assembly of inner-arm dynein IDA b and the beak-MIP structures. In addition, our functional studies reveal that loss of PACRG and/or FAP20 causes severe cell motility defects and reduced in vitro microtubule sliding velocities. Interestingly, the addition of exogenous PACRG and/or FAP20 protein to isolated mutant axonemes restores microtubule sliding velocities, but not ciliary beating. Taken together, these studies show that PACRG and FAP20 comprise the inner junction bridge that serves as a hub for both directly modulating dyneindriven microtubule sliding, as well as for the assembly of additional ciliary components that play essential roles in generating coordinated ciliary beating.

Original languageEnglish (US)
Pages (from-to)1805-1816
Number of pages12
JournalMolecular biology of the cell
Issue number15
StatePublished - Jul 15 2019

ASJC Scopus subject areas

  • Molecular Biology
  • Cell Biology


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