ANKEF1

ANKEF1 (ANKRD5) is an axonemal protein required for sperm motility that maintains the structural integrity of flagellar doublet microtubules (PMID:41460250). It is a component of the sperm axoneme that physically associates with the nexin-dynein regulatory complex (N-DRC) through calcium-independent interactions with its DRC5/TCTE1 and DRC4/GAS8 subunits (PMID:41460250). Loss of ANKEF1 in mice causes male infertility and impaired sperm motility; cryo-electron tomography of knockout sperm shows a structurally intact 9+2 axoneme but with pronounced morphological variability and increased structural heterogeneity of doublet microtubules, while ATP, reactive oxygen species, and mitochondrial membrane potential are unaffected — placing ANKEF1 in N-DRC mechanical buffering between adjacent doublets rather than in energy metabolism (PMID:41460250). In zebrafish, the ortholog Ankef1a localizes in a regionalized pattern along the proximal-distal axis of sensory hair-cell kinocilia, consistent with a broader role at motile/sensory ciliary axonemes (PMID:37367482). Beyond these findings, no additional mechanistic detail has been characterized in the available corpus.

1. 2023 Medium

   Before functional studies, it was unknown where ANKEF1 acts; localization of the zebrafish ortholog to hair-cell kinocilia established a ciliary/axonemal context for the protein.

   Evidence Transgenic zebrafish expressing fluorescently tagged Ankef1a with live imaging of kinocilial localization

   PMID:37367482

   Open questions at the time

   • No loss-of-function phenotype reported for Ankef1a in zebrafish
   • Functional significance of the regionalized kinocilial localization unresolved
   • No molecular partners identified in this system
2. 2024 Medium

   To define ANKEF1's molecular role, its interactions and the consequences of its loss were probed, identifying it as an N-DRC-associated axonemal protein required for sperm motility.

   Evidence Co-IP for N-DRC interactions, Ankrd5-/- knockout mouse fertility phenotype, cryo-electron tomography, and metabolic assays (preprint)

   PMID:bio_10.1101_2024.12.03.626701

   Open questions at the time

   • Preprint not yet peer-reviewed at this stage
   • Direct versus indirect nature of N-DRC interactions not fully resolved
   • Mechanism of doublet stabilization not directly demonstrated
3. 2025 High

   Peer-reviewed work confirmed ANKEF1 binds DRC5/TCTE1 and DRC4/GAS8 calcium-independently and is required to maintain doublet microtubule structural homogeneity, establishing a mechanical-buffering role distinct from axonemal energetics.

   Evidence Co-IP, Ankef1-/- knockout mouse with infertility/motility phenotype, cryo-electron tomography of axoneme ultrastructure, and ATP/ROS/mitochondrial membrane potential assays

   PMID:41460250

   Open questions at the time

   • Stoichiometry and structural position of ANKEF1 within the N-DRC not resolved
   • Whether ANKEF1 contributes to motile cilia outside sperm not addressed
   • Molecular mechanism linking N-DRC association to doublet structural homogeneity not directly demonstrated

• How ANKEF1 mechanistically stabilizes doublet microtubules and whether it functions in sensory/motile cilia beyond the sperm flagellum remains open.
• No structural model of ANKEF1 within the N-DRC
• Human disease link not established in the corpus
• Functional role at hair-cell kinocilia not tested by loss-of-function