DNAH6

DNAH6 is an inner dynein arm (IDA) heavy chain that powers motility of both respiratory cilia and sperm flagella and is required for normal ciliary beating and left-right body patterning (PMID:26918822). Loss of DNAH6 disrupts motile cilia in Kupffer's vesicle and respiratory epithelia across zebrafish and mammalian systems, producing heterotaxy with abnormal cardiac and gut looping, and DNAH6 acts genetically with other primary ciliary dyskinesia genes (DNAI1, DNAH5) such that subthreshold combined reduction causes laterality defects (PMID:26918822). Within the axoneme DNAH6 occupies defined proximal or distal positions that are progressively established during ciliogenesis as beating waveform matures (PMID:29851510). Its incorporation into the axoneme depends on the CCDC39/CCDC40 96 nm molecular ruler complex, since DNAH6 is absent from respiratory cilia in patients with CCDC39/CCDC40 variants (PMID:39056782). In the male germline DNAH6 is a testis-expressed protein localizing to the sperm neck, and its assembly into the sperm flagellar IDA is interdependent with other IDA heavy chains DNAH3 and DNAH7 (PMID:29356036, PMID:39503742, PMID:40810911). Biallelic DNAH6 variants abolish the protein and cause inner dynein arm and radial spoke loss together with sperm head defects—acephalic, globozoospermic, and vacuolated heads with abnormal acrosome biogenesis and chromatin compaction—and asthenoteratozoospermia (PMID:29356036, PMID:37594300, PMID:37424858).

1. 2016 High

   Established that DNAH6 is functionally required for motile cilia and left-right patterning, defining its core role rather than leaving it as an uncharacterized dynein gene.

   Evidence Morpholino knockdown in zebrafish and shRNA knockdown in human/mouse respiratory epithelia with ciliary motility and organ-looping readouts

   PMID:26918822

   Open questions at the time

   • Did not resolve which axonemal substructure DNAH6 builds
   • Mechanism of motility contribution at the molecular level not defined
2. 2016 High

   Showed DNAH6 contributes to laterality as a genetic modifier, explaining how subthreshold defects combine with other PCD genes to cause heterotaxy.

   Evidence Subthreshold double-morpholino epistasis in zebrafish and siRNA knockdown in heterozygous Dnah5/Dnai1 mutant mouse epithelia

   PMID:26918822

   Open questions at the time

   • Physical versus purely genetic interaction with DNAH5/DNAI1 not distinguished
   • Dosage thresholds in human disease not established
3. 2018 Medium

   Determined that DNAH6 occupies spatially defined axonemal positions set during ciliogenesis, linking its localization to maturation of beating waveform.

   Evidence Immunofluorescence in ex vivo and in vitro human airway cells correlated with high-speed video microscopy

   PMID:29851510

   Open questions at the time

   • Single lab
   • Trafficking mechanism that repositions DNAH6 not identified
4. 2018 Medium

   Extended DNAH6 function to the male germline, identifying it as a testis-specific neck-localized protein whose loss causes sperm head anomalies.

   Evidence Immunofluorescence, qRT-PCR, and whole-exome sequencing in patients with compound heterozygous variants

   PMID:29356036

   Open questions at the time

   • Single lab
   • Mechanism linking an IDA heavy chain to head formation unresolved
5. 2023 Medium

   Defined the structural consequences of DNAH6 loss in sperm, connecting it to IDA and radial spoke assembly as well as acrosome and chromatin defects.

   Evidence TEM, immunofluorescence, Western blot, and whole-exome sequencing in patient samples; identification of a homozygous frameshift causing asthenoteratozoospermia

   PMID:37424858 PMID:37594300

   Open questions at the time

   • Single lab cohorts
   • Causal chain from IDA defect to acrosome/chromatin abnormalities not mechanistically dissected
6. 2024 Medium

   Placed DNAH6 within the sperm flagellar inner dynein arm complex and showed its assembly is interdependent with other IDA heavy chains.

   Evidence Immunofluorescence and Western blot in DNAH3 knockout mice and patient spermatozoa showing co-reduced DNAH6, DNAH1, DNALI1

   PMID:39503742

   Open questions at the time

   • Direct physical interaction not demonstrated
   • Single lab
7. 2024 Medium

   Established that axonemal assembly of DNAH6 requires the CCDC39/CCDC40 96 nm ruler complex, defining its upstream dependency in respiratory cilia.

   Evidence Immunofluorescence of respiratory cilia in a cohort of 51 individuals with CCDC39/CCDC40 variants

   PMID:39056782

   Open questions at the time

   • Single lab
   • Whether DNAH6 binds the ruler directly or assembles downstream not resolved
8. 2025 Medium

   Confirmed DNAH6's IDA membership in sperm via co-dependency with DNAH7, distinguishing it from outer dynein arm components.

   Evidence Immunofluorescent staining and TEM of spermatozoa from patients with loss-of-function DNAH7 variants

   PMID:40810911

   Open questions at the time

   • Single lab
   • Order of IDA heavy chain assembly not established
9. 2025 Low

   Implicated transcriptional control of DNAH6 expression in spermatids by the POU4F2/Brn-3b factor.

   Evidence RNA-seq and qRT-PCR of Brn-3b knockout mouse testes (preprint)

   PMID:41282076

   Open questions at the time

   • No direct promoter binding or functional rescue for DNAH6 specifically
   • Single lab preprint, not peer-reviewed

• How DNAH6 is positioned and anchored at specific axonemal sites and how its loss mechanistically disrupts sperm head and acrosome biogenesis remain unresolved.
• No structural model of DNAH6 within the IDA
• No reconstitution of DNAH6 assembly
• Mechanistic link between flagellar IDA loss and head defects undefined