DNAH2

DNAH2 is an axonemal inner dynein arm heavy chain that drives microtubule sliding in motile cilia and sperm flagella. It functions as a subunit of the vertebrate Dynein-f complex together with intermediate chains WDR78 and WDR63, and its depletion paralyzes ependymal cilia in mouse and causes multiple morphological abnormalities of the sperm flagella (MMAF) with loss of inner dynein arms and central pair disorganization in human patients and knockout mice (PMID:30060180, PMID:33968937, PMID:30811583). Assembly of DNAH2 into axonemes requires CCDC40, and its transport through the sperm flagellar transition zone depends on CEP76 (PMID:35449766, PMID:38570187). DNAH2 also participates in nuclear DNA damage responses by facilitating FANCD2 ubiquitination and recruitment to interstrand crosslink repair sites in the Fanconi anemia pathway (PMID:35402838).

1. 2014 Low

   DNAH2 protein was confirmed as a structural component of axonemes in cilia and sperm flagella, establishing its identity as an axonemal dynein heavy chain prior to functional studies.

   Evidence ELISA and immunohistochemistry using VE1 antibody cross-reactivity against DNAH2 epitopes in human tissues

   PMID:25412847

   Open questions at the time

   • Only indirect evidence via antibody cross-reactivity, not a dedicated anti-DNAH2 reagent
   • No functional or loss-of-function data provided
   • Mechanistic role in the axoneme not addressed
2. 2019 High

   DNAH2 was established as a bona fide inner dynein arm component essential for ciliary and flagellar motility: it was shown to reside specifically in the inner dynein arm of human sperm, its loss caused inner dynein arm absence and axonemal disorganization, and it was identified as a Dynein-f heavy chain that associates with WDR78 and WDR63 to drive ciliary beat.

   Evidence Immunofluorescence/immunoblot on patient sperm with DNAH17 mutations (distinguishing inner vs. outer arms), TEM and whole-exome sequencing of DNAH2-mutant MMAF patients, co-immunoprecipitation of Dynein-f subunits plus RNAi knockdown in mouse ependymal cells and zebrafish morpholino experiments

   PMID:30060180 PMID:30811583 PMID:31178125

   Open questions at the time

   • Structural basis of DNAH2 interaction with WDR78/WDR63 not resolved
   • Contribution of DNAH2 versus other inner arm dyneins to specific beat patterns unknown
   • No cryo-EM or high-resolution structural data for the Dynein-f complex
3. 2021 High

   Knockout mouse and additional human genetic studies demonstrated that DNAH2 is essential for multiple steps of sperm flagellum assembly — not only inner dynein arm integrity but also centriolar protein organization, annulus positioning, and expression of other axonemal components such as DNAH1 and RSPH3.

   Evidence CRISPR/Cas9 Dnah2-knockout mice with SEM/TEM, immunofluorescence for centriolar and annulus markers, Western blot; TEM on sperm from patients with bi-allelic DNAH2 variants

   PMID:33771466 PMID:33968937

   Open questions at the time

   • Whether DNAH2 directly stabilizes DNAH1/RSPH3 or affects them indirectly through axonemal scaffold collapse is unresolved
   • How DNAH2 loss causes central pair defects is unknown
   • No rescue experiments in the mouse model
4. 2021 Medium

   An unexpected nuclear role was uncovered: DNAH2 facilitates FANCD2 ubiquitination and recruitment to DNA interstrand crosslink repair sites in the Fanconi anemia pathway, broadening its function beyond motile cilia.

   Evidence DNAH2 knockdown in U2OS cells with mitomycin C sensitivity assays, FANCD2 foci immunofluorescence, and ubiquitination assays

   PMID:35402838

   Open questions at the time

   • Mechanism by which a dynein heavy chain modulates FANCD2 ubiquitination is unexplained
   • Not independently replicated in a second lab or cell type
   • Whether DNAH2 localizes to the nucleus or acts indirectly is not established
5. 2022 Medium

   CCDC40 was placed upstream of DNAH2 in the inner dynein arm assembly pathway, as loss of CCDC40 function abolishes DNAH2 from both respiratory cilia and sperm flagella.

   Evidence Immunofluorescence on cilia and sperm from patients with CCDC40 variants, high-speed video microscopy

   PMID:35449766

   Open questions at the time

   • Whether CCDC40 directly interacts with DNAH2 or acts through an intermediate scaffold is not determined
   • Single study with limited patient numbers
6. 2024 Medium

   CEP76 was identified as a gatekeeper required for DNAH2 entry through the sperm flagellar transition zone, revealing the trafficking step that delivers DNAH2 to its site of action.

   Evidence Cep76 mutant mouse model with immunofluorescence showing DNAH2 accumulation at the sperm neck instead of the flagellum

   PMID:38570187

   Open questions at the time

   • Whether CEP76 acts directly on DNAH2 or on a shared transport carrier is unknown
   • Mechanism of transition zone gating for inner arm dyneins not defined
   • Single lab, no biochemical interaction data between CEP76 and DNAH2

• Key unresolved questions include the high-resolution structure of the DNAH2-containing Dynein-f complex, the molecular mechanism by which DNAH2 participates in FANCD2-mediated DNA repair, and whether the assembly and trafficking dependencies (CCDC40, CEP76) involve direct physical interactions with DNAH2.
• No cryo-EM or crystal structure of DNAH2 or its Dynein-f complex
• Nuclear localization and direct binding to FA pathway components not demonstrated
• Relative contribution of DNAH2 versus other inner arm dyneins to specific motility parameters in vivo is uncharacterized