IQUB

IQUB is a ciliary/flagellar scaffold protein whose principal characterized role is the assembly of radial spoke 1 (RS1) on the axoneme of mammalian sperm flagella (PMID:36417862, PMID:39849482). Genetic ablation in mice and humans selectively abolishes RS1 — leaving RS2 and RS3 intact — and co-depletes the inner dynein arm components DNAH7 and DNAH12, reducing sperm motility and causing asthenospermia and male infertility (PMID:36417862, PMID:39849482). IQUB localizes to the RS1 stalk and is one of twelve identified RS1 components, where it acts as an adapter that nucleates spoke assembly (PMID:39849482). It interacts with the radial spoke head protein RSPH3 as well as CEP295NL, GSTM1, and ODF1, and recruits calmodulin under low-Ca²⁺ conditions to suppress the activity of an RSPH3/p-ERK1/2 non-typical AKAP complex during spoke assembly (PMID:36355624). Within the male germline, IQUB protein localizes to the acrosome and flagellum of mature spermatozoa and is expressed across spermatogenic stages (PMID:37732581). Beyond the flagellum, IQUB regulates primary cilium length in somatic cells, acting downstream of ARL3 — re-expression of IQUB rescues the elongated-cilia phenotype of ARL3 mutant fibroblasts (PMID:21289087, PMID:38457249). IQUB also promotes breast cancer cell proliferation and migration by activating Akt-mediated GSK3β phosphorylation and downstream Wnt/β-catenin signaling, with its loss causing G1 cell cycle arrest (PMID:29968965).

1. 2011 Medium

   Established the first cellular function for IQUB by showing it constrains cilia length, identifying it as a ciliary regulator rather than an uncharacterized protein.

   Evidence siRNA knockdown with high-content immunofluorescence across three vertebrate cell lines and cargo transport assays

   PMID:21289087

   Open questions at the time

   • Molecular mechanism of length control not defined
   • No interacting partners identified
   • Single-lab knockdown without genetic confirmation
2. 2018 Medium

   Revealed a non-ciliary signaling role, linking IQUB to a proliferative cascade and showing it is not exclusively a structural ciliary protein.

   Evidence Overexpression and knockdown in MCF-7 and MDA-MB-231 cells with GSK3β and proteasome inhibitors, proliferation/migration and cell cycle assays

   PMID:29968965

   Open questions at the time

   • Direct biochemical link between IQUB and Akt not established
   • Mechanism connecting ciliary scaffold function to oncogenic signaling unclear
   • Single cancer-type context
3. 2022 High

   Defined IQUB's core structural function by showing it is selectively required for radial spoke 1 assembly in sperm flagella but dispensable for tracheal cilia spokes, explaining tissue-specific motility phenotypes.

   Evidence Iqub knockout mouse with TEM of sperm flagella and tracheal cilia and fertility assays

   PMID:36417862

   Open questions at the time

   • Reason for tissue selectivity (sperm vs trachea) not explained
   • Molecular interactions within RS1 not yet mapped
4. 2023 Medium

   Identified IQUB's direct binding partners and a calmodulin/Ca²⁺-dependent regulatory mechanism, providing the molecular basis for how it controls radial spoke assembly.

   Evidence Yeast two-hybrid screen, reciprocal Co-IP, KO/KI mouse models, EM, and whole-exome sequencing of patients

   PMID:36355624

   Open questions at the time

   • AKAP-inhibition mechanism partly inferred from inhibitor studies
   • Calmodulin recruitment not structurally resolved
   • Stoichiometry of interactions undefined
5. 2023 Medium

   Confirmed the subcellular distribution of IQUB protein in the male germline, localizing it to the acrosome and flagellum and across spermatogenic stages.

   Evidence Western blot and immunofluorescence with a newly generated antibody in wild-type mouse testis

   PMID:37732581

   Open questions at the time

   • No functional consequence tested in this study
   • Acrosomal role not mechanistically characterized
6. 2024 Medium

   Placed IQUB in an ARL3-dependent pathway controlling cilia length via epistasis, connecting its somatic ciliary function to an upstream regulator.

   Evidence Patient-derived ARL3 mutant fibroblasts, RNA-seq, proteomics, and IQUB rescue with cilia morphology measurement

   PMID:38457249

   Open questions at the time

   • Mechanism by which ARL3 regulates IQUB expression unknown
   • Whether ARL3 acts on IQUB in flagella as in somatic cilia untested
7. 2025 High

   Consolidated IQUB as an RS1 adapter/scaffold and defined RS1 composition, showing IQUB loss causes selective RS1 deficiency and co-dependent loss of inner dynein arm DNAH7/DNAH12 across human and mouse.

   Evidence Whole-exome sequencing of infertile males, Iqub-/- mouse, CASA, EM, mass spectrometry, structural modeling, and ICSI

   PMID:39849482

   Open questions at the time

   • Mechanism linking RS1 loss to inner dynein arm depletion not resolved
   • Structural model not experimentally validated
   • Order of assembly within RS1 stalk undefined

• How IQUB's structural role in radial spoke assembly mechanistically connects to its signaling functions in somatic cilia length control and Akt/Wnt-driven proliferation remains unresolved.
• No unifying biochemical mechanism across flagellar, ciliary, and oncogenic contexts
• Calmodulin/Ca²⁺ regulation not tested in somatic cilia
• No structural data on full-length IQUB complexes