KIF9

KIF9 is a plus-end-directed kinesin motor that operates at multiple microtubule-associated structures to control cell division, ciliary and flagellar function, and intracellular transport (PMID:40975050). In mitosis, KIF9 acts downstream of the RGK GTPase Gem, with which it physically interacts, to restrain microtubule polymerization and thereby set spindle length and ensure proper chromosome alignment (PMID:11483511, PMID:22964304). During interphase, KIF9 localizes to centriolar satellites and governs their pericentrosomal positioning; its loss causes satellite aggregation near the centrosome, increased degradation of centrosomal proteins, impaired centrosome maturation, and downstream chromosome congression and segregation defects (PMID:40975050), and this same satellite-positioning function supports primary cilium length and the maintenance of cilia proteins including TALPID3, CEP131, CEP170, and CEP290 (PMID:40879105). In the flagellar axoneme, KIF9 associates with central pair microtubules through the central pair component HYDIN to drive symmetric flagellar waveform and progressive sperm motility; loss-of-function abolishes KIF9 from sperm lacking HYDIN and produces asthenozoospermia in mice and humans (PMID:32072696, PMID:36686457). KIF9 additionally mediates anterograde lysosomal transport via kinesin light chain 1 (KLC1) to promote macroautophagy (PMID:39829171) and supports macrophage podosome matrix degradation through a C-terminal interaction with reggie-1/flotillin-2 (PMID:21119006).

1. 2001 Medium

   Established the first molecular link between an RGK-family GTPase and the microtubule motor machinery by identifying KIF9 as a Gem-binding partner, raising the question of what cytoskeletal process this interaction serves.

   Evidence Yeast two-hybrid screen with reciprocal co-immunoprecipitation

   PMID:11483511

   Open questions at the time

   • Did not define the functional consequence of the Gem-KIF9 interaction
   • No motor activity or directionality demonstrated
   • Single lab
2. 2010 Medium

   Showed KIF9 has a cytoskeletal-remodeling role beyond mitosis by linking its C-terminal region to podosome formation and matrix degradation in macrophages.

   Evidence siRNA/shRNA knockdown, overexpression, microinjection, and co-IP/colocalization with reggie-1/flotillin-2 in primary human macrophages

   PMID:21119006

   Open questions at the time

   • Mechanism by which flotillin-2 binding controls podosome activity unresolved
   • Cargo transported by KIF9 in this context not identified
   • Single lab
3. 2012 Medium

   Resolved the functional meaning of the Gem-KIF9 interaction, placing KIF9 as a downstream effector of Gem that limits microtubule polymerization to control spindle length and chromosome alignment.

   Evidence siRNA depletion with spindle length and tubulin polymerization measurements and Gem/KIF9 epistasis

   PMID:22964304

   Open questions at the time

   • Did not determine whether KIF9 restrains polymerization directly via motor activity or indirectly
   • No structural basis for the Gem-KIF9 interaction
   • Single lab
4. 2020 High

   Identified an axonemal role for KIF9 by showing it is required for progressive sperm motility and depends on the central pair component HYDIN for its localization.

   Evidence CRISPR/Cas9 knockout mouse with sperm motility analysis, immunofluorescence/immunoblot, and epistasis with HYDIN mutant

   PMID:32072696

   Open questions at the time

   • Did not define how KIF9 motor activity shapes the flagellar waveform
   • Direct binding partner within the central pair not pinpointed
5. 2023 Medium

   Extended the flagellar role to human disease, establishing bi-allelic KIF9 loss-of-function as a cause of asthenozoospermia and confirming the KIF9-HYDIN interaction in human samples.

   Evidence Whole exome sequencing of patients, co-IP, immunofluorescence, and transmission electron microscopy

   PMID:36686457

   Open questions at the time

   • Did not establish the structural mechanism of KIF9 at the central pair
   • Patient cohort limited
   • Single lab
6. 2025 High

   Defined KIF9 as a centriolar satellite regulator, showing satellite mispositioning upon its loss drives centrosomal protein degradation, impaired centrosome maturation, and mitotic chromosome defects.

   Evidence KIF9 knockdown/knockout with live-cell imaging, immunofluorescence, mass spectrometry proteomics, and centrosome maturation assays

   PMID:40975050

   Open questions at the time

   • Cargo and adaptors linking KIF9 to satellites not fully mapped
   • Relationship between satellite-positioning and the Gem-dependent spindle role not integrated
7. 2025 Medium

   Connected KIF9-controlled satellite positioning to ciliogenesis, showing its loss alters primary cilia length and levels of specific cilia proteins.

   Evidence KIF9 loss-of-function with cilia length measurement and western blot for TALPID3, CEP131, CEP170, CEP290

   PMID:40879105

   Open questions at the time

   • Did not establish whether the cilia protein changes are direct or secondary to satellite aggregation
   • Single lab
8. 2025 Medium

   Demonstrated a transport-and-clearance role for KIF9, showing it drives anterograde lysosomal transport via KLC1 to sustain macroautophagy, with therapeutic relevance in an Alzheimer's model.

   Evidence KIF9-KLC1 co-IP, live lysosome transport assay, and AAV-mediated overexpression with behavioral testing in APP23/PS45 mice

   PMID:39829171

   Open questions at the time

   • Did not establish whether KIF9 acts as a primary motor or accessory adaptor in lysosome transport
   • Generalizability beyond neurons unclear
   • Single lab

• How KIF9's distinct activities across spindle, centriolar satellites, axonemal central pair, podosomes, and lysosomal transport are coordinated and selected in different cell types remains unresolved.
• No unifying model linking motor directionality to its diverse cargoes
• No structural characterization of KIF9 motor or cargo-binding regions
• Cargo-selection mechanism unknown