IFT70A

IFT70A (TTC30A) is a peripheral subunit of the intraflagellar transport IFT-B complex required for ciliogenesis (PMID:29654116). It engages the IFT-B core through its TPR repeats and terminal α36 helix, binding the IFT52-IFT88 dimer; removing the first TPR or the α36 helix abrogates this interaction (PMID:29654116). IFT70A acts redundantly with its paralog IFT70B—single knockouts assemble cilia normally and other IFT-B subunits still localize to the ciliary base, but loss of both abolishes ciliogenesis, and either paralog rescues the defect (PMID:29654116). Beyond this structural role, loss of the IFT70A ortholog in Xenopus impairs ciliogenesis and renal excretion and alters posttranslational tubulin acetylation and glycylation with defective axoneme compartmentalization (PMID:34548398). A paralog-specific function distinguishes IFT70A from IFT70B: it interacts with the PKA catalytic subunit PRKACA and with IFT57, and a disease-associated mutant blocks ciliary entry of Smoothened independently of Patched1, leading to accumulation of phosphorylated PKA substrates and downregulation of Sonic hedgehog signaling without affecting cilium assembly (PMID:38074101).

1. 2018 High

   Established how IFT70A docks into the IFT-B complex and whether it is individually essential, resolving its structural role in ciliogenesis.

   Evidence CRISPR/Cas9 IFT70A/B double-knockout cells with rescue, TPR and α36 deletion mutagenesis, and interaction/ciliogenesis assays

   PMID:29654116

   Open questions at the time

   • Does not define functional differences between IFT70A and IFT70B given full redundancy here
   • No structural model of the IFT52-IFT88-IFT70A interface
   • Mechanism of how IFT70A loss blocks ciliogenesis at the molecular level not resolved
2. 2019 Low

   Showed IFT70A localizes to sperm flagella and that its localization depends on TTC29, extending its role beyond primary cilia.

   Evidence Immunofluorescence of human spermatozoa from biallelic TTC29 mutation carriers and a Ttc29-mutant mouse

   PMID:31735294

   Open questions at the time

   • Single immunofluorescence observation secondary to a TTC29-focused study; not independently validated
   • Whether TTC29 and IFT70A interact directly is unknown
   • No functional consequence of altered IFT70A flagellar localization defined
3. 2021 Medium

   Connected IFT70A loss to altered tubulin posttranslational modifications and axoneme compartmentalization in a vertebrate, linking it to ciliopathy phenotypes.

   Evidence CRISPR/Cas9 mutagenesis in Xenopus tropicalis with immunofluorescence for tubulin acetylation/glycylation and analysis of cilia and kidney

   PMID:34548398

   Open questions at the time

   • Whether tubulin modification changes are direct or downstream of impaired transport is unresolved
   • Single lab, single model organism
   • No mechanism linking IFT70A to the modifying enzymes
4. 2023 Medium

   Defined a paralog-specific role for IFT70A in Hedgehog signaling distinct from its structural IFT-B function, via PRKACA and IFT57 interactions and Smoothened regulation.

   Evidence TTC30A/B knockout RPE1 cells with wildtype/mutant rescue, mass spectrometry interactome, Smoothened localization, and forskolin PKA-substrate phosphorylation assays

   PMID:38074101

   Open questions at the time

   • Direct vs indirect nature of the PRKACA interaction not biochemically resolved
   • Mechanism by which the mutant blocks Smoothened ciliary entry independent of Patched1 unknown
   • Single lab; disease relevance of the mutant beyond cell models not established
5. 2025 Low

   Showed IFT70A mature-sperm localization and abundance depend on TULP2, further defining flagellar regulation of IFT70A.

   Evidence Immunofluorescence localization and quantitative protein analysis in Tulp2-knockout mouse spermatids and spermatozoa

   PMID:40613306

   Open questions at the time

   • Localization finding is secondary to a TULP2-focused study; single method
   • Whether TULP2 acts directly on IFT70A is unknown
   • Stage specificity (spermatozoa but not spermatids) is unexplained mechanistically

• How IFT70A-specific interactions are partitioned from its redundant IFT-B structural role, and the molecular basis of its Hedgehog-modulating and tubulin-modification effects, remain open.
• No structural model of IFT70A within an assembled IFT-B train
• Direct enzymatic or adaptor mechanism for tubulin modification changes unknown
• Biochemical basis of paralog-specific PRKACA/IFT57 engagement not defined