POC1B

POC1B is a centriolar inner-scaffold protein that maintains centriole microtubule integrity, supports centriole duplication, and is required for ciliogenesis across tissues (PMID:23015594, PMID:39543170). It forms heterodimers with POC1A within the centriole lumen, where its WD40 domain localizes close to the centriole wall and the heterodimer organizes an inner-scaffold interaction network with the microtubule-binding proteins FAM161A and MDM1 that position POC5; disruption of POC1B alone causes centriole microtubule defects, whereas loss of both POC1A and POC1B causes centriole disintegration (PMID:39543170). POC1B localizes to centrioles, spindle poles, and the basal body of primary and photoreceptor sensory cilia, and its interaction with the connecting-cilium protein FAM161A is required for basal body targeting (PMID:25018096, PMID:25044745). Beyond a centriole-integrity role redundant with POC1A, POC1B is specifically phosphorylated during mitosis and is independently required for normal cell proliferation (PMID:23015594). POC1B function is essential in specialized ciliated cells: a homozygous frameshift variant abolishes sperm POC1B and causes oligoasthenoteratozoospermia with abnormal acrosome and flagella formation in knock-in mice (PMID:37070736), and disease-associated POC1B variants that disrupt basal body localization and FAM161A binding underlie retinal and ciliopathy phenotypes (PMID:25018096, PMID:25044745). POC1B protein levels are also set post-transcriptionally, with HNRNPH1-mediated o8G oxidation repressing POC1B mRNA to control centrosome integrity in cardiomyocytes (PMID:41325109).

1. 2012 High

   Establishing whether POC1B acts only redundantly with its paralog defined its dual role: it maintains nascent centriole integrity together with POC1A but also has an independent, mitosis-specific function.

   Evidence Isoform-specific antibody localization, FRAP, RNAi co-depletion and mitotic progression assays in human cells

   PMID:23015594

   Open questions at the time

   • Molecular target of the mitosis-specific phosphorylation and the kinase responsible were not identified
   • The mechanistic basis of the proliferation defect independent of centriole integrity was not resolved
2. 2014 High

   Identifying a direct POC1B-FAM161A interaction and showing disease variants abolish basal body localization connected POC1B to connecting-cilium biology and human ciliopathy.

   Evidence Yeast two-hybrid, reciprocal Co-IP, colocalization in RPE1 cells, and zebrafish morpholino rescue, with two missense/deletion variants tested

   PMID:25018096

   Open questions at the time

   • Structural interface between POC1B and FAM161A not defined
   • How loss of the interaction translates into ciliary dysfunction at the molecular level unresolved
3. 2014 Medium

   Localization to photoreceptor basal body and connecting cilium with in vivo knockdown phenotypes tied POC1B loss to retinal degeneration and broader ciliopathy.

   Evidence Immunofluorescence in human/mouse retina and zebrafish morpholino knockdown

   PMID:25044745 PMID:26188096

   Open questions at the time

   • Morpholino phenotypes not confirmed with stable genetic mutants
   • Synaptic outer-plexiform-layer localization role not mechanistically characterized
4. 2019 Medium

   Genetic epistasis in Drosophila sperm showed POC1B is recruited to centriole/PCL cores in a Sas-6-dependent manner and reciprocally stabilizes Sas-6-dependent structures, placing it in the centriole-assembly hierarchy.

   Evidence Co-localization, genetic co-overexpression, and Poc1 mutant analysis in Drosophila

   PMID:31387336

   Open questions at the time

   • Whether the same Sas-6 dependency operates in mammalian centriole assembly not tested
   • Biochemical nature of POC1B-Sas-6 stabilization unknown
5. 2023 High

   A patient frameshift variant modeled in knock-in mice established POC1B as essential for mammalian sperm flagella and acrosome formation, extending its requirement to motile ciliogenesis.

   Evidence Whole-exome sequencing, patient sperm protein analysis, CRISPR knock-in mice, testicular histology and TEM

   PMID:37070736

   Open questions at the time

   • Molecular step in flagellar assembly that requires POC1B not pinpointed
   • Relationship between sperm defects and the inner-scaffold function not directly connected
6. 2024 High

   Mapping the POC1A-POC1B heterodimer and its WD40 domain orientation within the centriole lumen resolved how POC1B organizes the inner scaffold via FAM161A, MDM1 and POC5.

   Evidence Co-IP, super-resolution localization mapping, and genetic deletion with ultrastructural phenotypes in human cells

   PMID:39543170

   Open questions at the time

   • High-resolution structure of the assembled scaffold not solved
   • How the scaffold mechanically reinforces centriole microtubules not defined
7. 2026 Medium

   Discovery that HNRNPH1 represses POC1B mRNA through o8G oxidation, antagonized by a piRNA, revealed post-transcriptional control of POC1B as a lever for centrosome integrity and cardiomyocyte proliferation.

   Evidence Mass spectrometry, RNA pull-down, o8G-RIP-seq, and cardiomyocyte-specific HNRNPH1 knockout and piRNA manipulation in mice

   PMID:41325109

   Open questions at the time

   • Direct demonstration that POC1B restoration alone rescues the cardiac phenotype not established
   • Whether o8G regulation of POC1B operates outside cardiomyocytes unknown

• The molecular identity and consequence of the mitosis-specific POC1B phosphorylation that drives its centriole-independent proliferation role remain undefined.
• Responsible kinase and phosphosites unknown
• Mechanistic link between phosphorylation and cell cycle progression unresolved