DNAAF6

DNAAF6 (PIH1D3) is a cytoplasmic PIH-domain co-chaperone that drives the cytoplasmic preassembly of axonemal dynein complexes destined for cilia and sperm flagella (PMID:24421334). It operates within an R2TP-like HSP90 co-chaperone module, physically associating with the dynein-assembly factors DNAAF2 and DNAAF4 to build both outer (ODA) and inner (IDA) dynein arms before their import into the axoneme (PMID:28041644, PMID:28176794). Consistent with this preassembly role, loss of DNAAF6 abolishes ODAs and reduces or eliminates IDAs, yielding immotile cilia and flagella (PMID:24421334, PMID:28041644); this requirement is conserved through Drosophila, where Dnaaf6 and Dnaaf4 form an analogous dynein-assembly complex (PMID:35873488). Beyond dynein chaperoning, DNAAF6 interacts with LARP6 and co-localizes in biomolecular condensates (dynein axonemal particles) in multiciliated cells, where this interaction is required for high apical α-tubulin expression during ciliogenesis (PMID:38762183). Loss-of-function mutations cause X-linked primary ciliary dyskinesia, with the spectrum of situs inversus, hydrocephalus, defective mucociliary clearance, and male infertility documented across patient cohorts and knockout rodent models (PMID:28176794, PMID:32170493, PMID:37900281); in heterozygous female carriers, skewed X-inactivation governs the fraction of dynein-deficient cilia and thereby the variable expressivity of disease (PMID:38408845).

1. 2014 High

   Established that DNAAF6 is a cytoplasmic factor required for preassembly of axonemal dynein arms rather than an axonemal structural component, answering where and when it acts in dynein biogenesis.

   Evidence Knockout mouse with cytoplasmic localization imaging, axoneme EM showing absent ODA/IDA, and Co-IP with ODA intermediate chain, Hsp70, and Hsp90

   PMID:24421334

   Open questions at the time

   • Did not define the specific dynein subunits stabilized at the molecular level
   • Stoichiometry and architecture of the chaperone complex not resolved
2. 2016 High

   Connected DNAAF6 to human disease and placed it in a defined cytoplasmic assembly module by showing physical association with DNAAF2 and DNAAF4.

   Evidence Patient loss-of-function mutations, TEM of cilia ultrastructure, and reciprocal Co-IP with DNAAF2 and DNAAF4

   PMID:28041644

   Open questions at the time

   • Direct demonstration of an assembled ternary complex not provided
   • Mechanism by which IDA subsets are differentially affected unresolved
3. 2017 Medium

   Defined the X-linked genetic basis of DNAAF6-associated PCD and proposed its function within an R2TP-like HSP90 co-chaperone complex affecting a subset of inner-arm dyneins.

   Evidence Genomic deletion mapping, point-mutation sequencing, and immunofluorescence of dynein markers in patient cilia

   PMID:28176794

   Open questions at the time

   • R2TP-like complex membership proposed but not reconstituted
   • Which IDA species require DNAAF6 versus the parallel DNAAF2/DNAAF4 pathway not delineated
4. 2020 Medium

   Clarified the molecular consequence of pathogenic alleles by showing missense and frameshift variants destabilize the DNAAF6 protein.

   Evidence HEK293T expression assay demonstrating protein degradation, plus TEM of patient sperm and immunostaining

   PMID:32170493

   Open questions at the time

   • Degradation pathway and turnover mechanism not identified
   • Single-lab assay; only two variants tested
5. 2022 Medium

   Demonstrated evolutionary conservation of the DNAAF6-DNAAF4 dynein-assembly complex, showing the function is retained even where the TPR/HSP90-recruitment domain is absent.

   Evidence Drosophila genetic knockout with chordotonal and sperm phenotyping, sperm axoneme EM, and complex co-association by mass spectrometry

   PMID:35873488

   Open questions at the time

   • How HSP90 is engaged without a TPR domain in Drosophila unexplained
   • Whether the fly complex assembles the same dynein subsets as in mammals untested
6. 2023 Medium

   Confirmed the dynein preassembly and uploading role in an independent mammalian model and broadened the in-vivo phenotype to hydrocephalus, situs inversus, and spermatocyte defects.

   Evidence TALEN knockout rat with pathological phenotyping, Co-IP identifying dynein-arm assembly partners, and EM analysis

   PMID:37900281

   Open questions at the time

   • Novel interacting partners not individually validated reciprocally
   • Mechanism linking dynein loss to communicating hydrocephalus not dissected
7. 2024 Medium

   Revealed a chaperone-independent function: DNAAF6 partners with LARP6 in axonemal condensates to support apical α-tubulin expression during multiciliated-cell ciliogenesis.

   Evidence Xenopus morphant rescue with a LARP6-binding-deficient mutant, condensate co-localization, and α-tubulin immunofluorescence readout

   PMID:38762183

   Open questions at the time

   • Mechanism by which the condensate elevates α-tubulin translation unresolved
   • Whether this role operates in mammalian cilia not tested
8. 2024 Medium

   Explained variable expressivity in female carriers by linking skewed X-inactivation to the proportion of dynein-deficient airway cilia.

   Evidence DNA-methylation XCI assay, airway cilia immunofluorescence and high-speed videomicroscopy across 6 families

   PMID:38408845

   Open questions at the time

   • Threshold of functional cilia derived from correlation, not mechanistic intervention
   • Tissue-specific XCI variation across organs not assessed
9. 2025 Medium

   Extended the pathogenic mutation spectrum to a splice-disrupting intronic variant causing exon skipping and dynein-arm loss.

   Evidence Minigene splicing assay confirming exon 6 skipping plus TEM of patient sperm flagella

   PMID:41480157

   Open questions at the time

   • Single family; functional rescue not performed
   • Residual transcript/protein levels not quantified

• How DNAAF6 selects and stabilizes specific dynein arm subunits, and how its R2TP-like chaperone activity is mechanistically coordinated with the LARP6-condensate tubulin pathway, remains unresolved.
• No reconstituted R2TP-like complex with defined stoichiometry
• Substrate specificity for distinct ODA/IDA subtypes uncharacterized
• No structural model of DNAAF6 in either chaperone or condensate context