LRRCC1

LRRCC1 is a leucine-rich repeat and coiled-coil domain protein that localizes asymmetrically within the distal lumen of centrioles and basal bodies, where it establishes rotational asymmetry and maintains centriole structural integrity (PMID:11285274, PMID:35319462). In human cells, LRRCC1 occupies two consecutive triplets of the distal centriolar lumen, partially co-localizes with C2CD3 in an acorn-like structure, and is required for proper ciliogenesis and ciliary signaling; its depletion causes multipolar spindles, centrosome splitting, and defective ciliary assembly (PMID:18728398, PMID:35319462). In multiciliated epithelia, LRRCC1 is essential for basal body docking, spacing, rotational polarization, and cilia-driven fluid flow (PMID:35067717). Across species from Chlamydomonas to planarians and vertebrates, LRRCC1/Vfl1 orthologs are required for centriole appendage assembly and the bilaterally symmetric orientation of basal bodies (PMID:11285274, PMID:31743665).

1. 2001 High

   Identification of the Chlamydomonas VFL1 gene product established that a leucine-rich repeat/coiled-coil protein resides asymmetrically in the distal basal body lumen and is required for correct rotational orientation of basal bodies, providing the first molecular handle on centriolar rotational asymmetry.

   Evidence Epitope-tagged rescue, immunogold EM, and co-purification with basal body apparatuses in Chlamydomonas

   PMID:11285274

   Open questions at the time

   • Whether the mammalian ortholog shares the same localization and function was unknown
   • Direct interacting partners within the basal body lumen were not identified
   • How Vfl1 asymmetric positioning is established remained unresolved
2. 2008 High

   Characterization of the human ortholog CLERC/LRRCC1 demonstrated that the protein associates with centrosomes throughout the cell cycle and is required to prevent centrosome splitting and multipolar spindle formation, extending the centriolar integrity function to mammalian cells.

   Evidence RNAi depletion in human cells with immunofluorescence and spindle pole analysis

   PMID:18728398

   Open questions at the time

   • Sub-centriolar localization at nanometer resolution was not determined
   • Whether LRRCC1 is required for ciliogenesis in mammalian cells was untested
   • Mechanism by which LRRCC1 loss causes centrosome splitting was unknown
3. 2019 Medium

   Work in planaria showed that the LRRCC1 ortholog SMED-VFL1 is required for centriole appendage assembly and bilaterally symmetric patterning of centrioles across tissues, generalizing the rotational asymmetry function to a metazoan context.

   Evidence RNAi knockdown in planarian ventral epidermis with centriole positioning analysis

   PMID:31743665

   Open questions at the time

   • Single study in a non-standard model organism; independent confirmation in other metazoans needed
   • The molecular targets or appendage components regulated by SMED-VFL1 were not identified
   • Relationship to ciliary function in planaria was not directly assessed
4. 2022 High

   Super-resolution expansion microscopy revealed that LRRCC1 occupies two consecutive triplets of the human distal centriolar lumen and cooperates with C2CD3 in an acorn-like structure required for centriole integrity, ciliogenesis, and ciliary signaling, resolving the nanoscale architecture and linking LRRCC1 to the ciliary signaling pathway.

   Evidence U-ExM, RNAi depletion, co-localization/co-recruitment assays, and Hedgehog signaling readouts in human cells

   PMID:35319462

   Open questions at the time

   • Whether LRRCC1 directly binds C2CD3 or is co-recruited independently was unresolved
   • The full molecular composition of the human acorn structure was not determined
   • Structural basis for LRRCC1 asymmetric positioning on specific triplets was unknown
5. 2022 High

   Functional studies in Xenopus multiciliated cells established that Lrrcc1 at the basal body proximal junction is essential for basal body docking, spacing, rotational polarization, and cilia-driven fluid flow, demonstrating its requirement in motile cilia function.

   Evidence Morpholino knockdown in Xenopus embryonic ciliated epidermis with beat frequency and flow assays

   PMID:35067717

   Open questions at the time

   • Whether basal body docking defects are secondary to loss of rotational asymmetry or a separable function was not distinguished
   • Interaction partners at the proximal junction/rootlet interface were not identified
6. 2025 Medium

   Epistatic KO analysis placed LRRCC1 downstream of C2CD3 and SSNA1 in a hierarchical targeting axis for distal lumen organization, defining the recruitment logic for the human acorn complex.

   Evidence (preprint) KO-validated antibodies, interactor screening, expansion microscopy, and epistatic KO analysis in human cells

   PMID:bio_10.1101_2025.04.28.648957

   Open questions at the time

   • Preprint not yet peer-reviewed
   • Whether SSNA1 directly recruits LRRCC1 or acts indirectly through C2CD3 was not resolved
   • Structural basis for the hierarchical targeting was not determined

• The direct binding interfaces among LRRCC1, C2CD3, and SSNA1, the structural basis for LRRCC1's asymmetric positioning on specific centriolar triplets, and whether LRRCC1 mutations are causative for human ciliopathies remain to be established.
• No crystal or cryo-EM structure of LRRCC1 or the acorn complex exists
• No confirmed causative LRRCC1 mutations in human disease families
• Mechanism by which LRRCC1 loss leads to multipolar spindles is unknown