Distinct learning-progression job: Learn how animal cells build exactly one daughter centriole beside each existing centriole by following PLK4 recruitment and self-regulation, STIL phosphorylation, SAS6 cartwheel symmetry, CPAP-linked microtubule growth, daughter maturation and the cell-cycle licensing logic that prevents both centriole loss and overduplication.
Canonical boundary: Cell Cycle and Checkpoints remains the broad owner of cell-cycle control; Cytoskeleton and Molecular Motors remains the broad owner of microtubule mechanics; Cilia and Flagella and Intraflagellar Transport and Cilia remain ciliary owners. This article owns human/animal centriole duplication: PLK4–STIL–SAS6-driven procentriole initiation, ninefold cartwheel construction, elongation and once-per-cell-cycle number control.
Reader-safety boundary: General cell biology and developmental biology only. Disease/cancer examples are mechanistic.
Wait, What? A Cell Must Copy an Organelle Exactly Once Without a DNA Template
DNA replication has base pairing. Centrioles have no equivalent sequence template.
Yet a dividing animal cell must normally create one new procentriole beside each old centriole.
Too few centrioles can compromise spindle organization and ciliogenesis. Too many can create extra centrosomes and chromosome-segregation problems.
The central question is therefore:
How does a self-assembling protein machine build one ninefold-symmetric daughter at one site, once per cell cycle?
The One-Sentence Answer
Learn centriole duplication as a spatially restricted self-assembly programme: CEP192 and CEP152 recruit and activate PLK4 around the proximal region of a parent centriole, PLK4 self-organizes and is normally limited by autophosphorylation-dependent turnover, a single productive PLK4 focus phosphorylates STIL, phosphorylated STIL recruits and organizes SAS6 into the ninefold cartwheel, CPAP/CEP135 and tubulin build the procentriole wall, and later centriole disengagement/licensing plus tightly controlled protein turnover reset the system so duplication can occur once again in the next cell cycle.
Learning Ladder
Beginner: centrioles duplicate once per cell cycle so cells can maintain the correct centrosome number.
Secondary / Pre-University: centrosomes, microtubules, cell division, phosphorylation, protein degradation and symmetry.
Undergraduate: PLK4, CEP192, CEP152, STIL, SAS6, CPAP, CEP135, CP110, β-TrCP and centriole disengagement.
Advanced / Professional: PLK4 ring-to-focus symmetry breaking, kinase autophosphorylation, STIL STAN-domain phosphorylation, SAS6 oligomerization, cartwheel-to-microtubule coupling, daughter-to-mother conversion, separase/PLK1 licensing, centriole amplification and ultrastructural mapping by expansion microscopy/cryo-ET.
Stage Progression
1. Separate centriole from centrosome
A centrosome usually contains a centriole pair plus surrounding pericentriolar material.
2. A centriole has ninefold radial symmetry
Its microtubule wall is organized around a characteristic ninefold architecture.
3. Duplication begins near the proximal parent-centriole region
A new procentriole forms orthogonally adjacent to each existing parent.
4. PLK4 is the master initiation kinase
Changing PLK4 abundance strongly changes centriole number.
5. CEP192 and CEP152 recruit PLK4
These scaffolds position PLK4 around the parent centriole.
6. CEP152 can also stimulate PLK4 activation
2025 work showed CEP152 binding can increase PLK4 phosphorylation and kinase activity.
7. PLK4 initially forms a broader ring-like distribution
Early in duplication, PLK4 can occupy multiple sites around the parent centriole.
8. The system breaks symmetry
A single dominant PLK4 focus is selected as the productive procentriole site.
9. PLK4 limits itself through autophosphorylation
PLK4 can trans-autophosphorylate degron regions.
10. β-TrCP-dependent turnover prevents excess PLK4
SCF–β-TrCP-related degradation keeps PLK4 abundance low and limits overduplication.
11. Self-destruction is part of accurate organelle copying
The initiator is powerful because it is transient.
12. STIL activates and becomes a substrate of PLK4
STIL binds PLK4 and helps activate kinase activity.
13. PLK4 phosphorylates the STIL STAN domain
This creates the state that recruits SAS6 efficiently.
14. SAS6 builds the cartwheel
SAS6 proteins oligomerize through head and coiled-coil interactions.
15. Cartwheel geometry generates ninefold symmetry
The central hub and spokes organize the radial architecture of the future centriole.
16. Ninefold symmetry emerges from molecular geometry
The parent centriole does not simply stamp a daughter copy.
17. STIL links the cartwheel to wall growth
Additional PLK4-dependent STIL phosphorylation promotes interaction with CPAP.
18. CPAP controls microtubule-wall assembly and length
CPAP helps organize centriolar microtubules around the cartwheel.
19. CEP135 supports cartwheel-to-wall coupling
CEP135 contributes structural linkage between SAS6/cartwheel elements and the microtubule cylinder.
20. Procentriole elongation is regulated
A daughter must grow enough to become functional without overelongating.
21. CP110 caps distal-end growth
CP110 and associated proteins help restrain excessive centriole elongation.
22. Daughter centrioles are initially immature
A newly built daughter cannot immediately perform every mature mother-centriole job.
23. Maturation spans more than one cell-cycle phase
Distal/subdistal appendages and full centrosomal competence develop later.
24. Mother-centriole identity matters for ciliogenesis
Only sufficiently mature centrioles can efficiently become basal bodies for primary cilia.
25. Duplication must be licensed once per cycle
Existing mother–daughter pairs remain engaged, helping prevent immediate reduplication.
26. Disengagement resets competence
Separase- and PLK1-linked events around mitotic exit help disengage centriole pairs.
27. Disengagement is not instant duplication
It licenses a future round, but actual procentriole formation still requires S-phase PLK4/STIL/SAS6 machinery.
28. Cell-cycle protein abundance controls timing
STIL and SAS6 levels change across the cycle, adding another temporal gate.
29. STIL–SAS6 must also be cleared
2026 work implicates FBXW7-mediated turnover of PLK4-phosphorylated STIL–SAS6 assemblies in preventing overduplication.
30. Too little initiation produces centriole loss
PLK4/STIL/SAS6 depletion can create acentriolar cells.
31. Too much initiation produces centriole amplification
PLK4 overexpression or failed turnover can produce multiple procentrioles.
32. Extra centrioles can produce extra spindle poles
Cells may cluster extra centrosomes, but this increases division complexity and chromosome-segregation risk.
33. Centriole amplification is not identical to centrosome amplification
Extra centrioles can mature into extra centrosomes later.
34. Centriole defects can alter brain development
Mutations in several centriole genes are associated with primary microcephaly and related developmental disorders.
35. Centriole defects also alter cilia
Because mature centrioles become basal bodies, duplication defects can propagate into ciliary phenotypes.
36. Expansion microscopy reveals assembly order
Ultrastructure expansion microscopy can map many proteins with nanometre-scale spatial resolution over time.
37. Cryo-ET reveals native cartwheel and wall architecture
Structural imaging helps connect protein localization with physical centriole geometry.
38. Professional closure test
Ask where PLK4 was recruited, whether one focus won symmetry breaking, whether STIL was correctly phosphorylated, whether SAS6 built one cartwheel, whether CPAP/CEP135 assembled a normal wall, whether protein turnover suppressed extra sites, and whether the daughter matured and licensed correctly for the next cycle.
Evidence: What Proves What?
Initiation
- PLK4 localization;
- CEP152/CEP192 perturbation;
- PLK4 kinase mutants.
Cartwheel formation
- STIL phosphorylation;
- SAS6 recruitment;
- ultrastructure expansion microscopy;
- cryo-ET.
Number control
- PLK4 turnover;
- β-TrCP/FBXW7 perturbation;
- procentriole counting.
Elongation
- CPAP/CEP135/CP110 perturbation;
- electron microscopy;
- centriole length measurements.
Cell-cycle licensing
- disengagement assays;
- separase/PLK1 perturbation;
- mother–daughter tracking.
Connections Worth Making
Cell Cycle
Centriole duplication is coordinated with S phase and mitotic exit.
Protein Degradation
Accuracy depends on destroying PLK4 and limiting STIL–SAS6 assemblies.
Self-Assembly
Ninefold symmetry emerges from SAS6/cartwheel geometry.
Cytoskeleton
Centriolar microtubules are specialized, highly stable microtubule structures.
Cilia
A mature centriole can become a basal body.
Misconceptions Worth Hunting
- “The centrosome duplicates by splitting in half.” New procentrioles are assembled beside existing centrioles.
- “The parent centriole physically templates every daughter microtubule.” Molecular self-assembly is central.
- “PLK4 should be maximized to ensure duplication.” Excess PLK4 causes overduplication.
- “SAS6 is the kinase.” PLK4 is the kinase; SAS6 is a cartwheel structural protein.
- “Ninefold symmetry comes from nine DNA sequences.” It emerges from protein geometry.
- “A new daughter centriole is immediately a mature mother centriole.” Maturation takes time.
- “Disengagement itself creates a new centriole.” It licenses the next duplication round.
- “Extra centrioles and extra centrosomes are always identical states.” Maturation determines centrosomal competence.
Transfer Check
PLK4 is overexpressed around one parent centriole. What risk rises? Multiple procentrioles and centriole amplification.
STIL reaches the parent centriole but cannot be phosphorylated in its SAS6-recruiting region. What fails? Efficient cartwheel initiation.
SAS6 builds abnormal oligomers. Which feature is most directly threatened? Ninefold cartwheel symmetry.
A daughter centriole forms but never matures. Can ciliary basal-body function be impaired later? Yes.
Centrioles disengage normally but PLK4 is inhibited in the next S phase. Does licensing guarantee duplication? No.
How We Know the Learning Has Held
A learner should be able to distinguish centriole from centrosome; explain PLK4 recruitment and self-limiting turnover; trace PLK4→STIL→SAS6; explain ninefold cartwheel self-assembly; connect CPAP/CEP135 with wall growth; explain daughter maturation; explain disengagement/licensing; and diagnose underduplication versus overduplication from evidence.
Model Limits
Species differ in centriole proteins and geometry. Ring-to-focus models are best defined in selected animal cells. PLK4 organization is dynamic and technique-sensitive. Cartwheel structures vary across lineages. Protein degradation systems are partially redundant. Centrosome amplification can arise through centriole overduplication, failed cytokinesis and other routes.
Professional centriole reasoning keeps parent identity + PLK4 spatial state + kinase activity + STIL/SAS6 cartwheel state + microtubule-wall growth + turnover + cell-cycle licensing visible together.
Teaching Guide
Teach in this order:
centriole architecture → centrosome → PLK4 → CEP192/CEP152 → PLK4 symmetry breaking → PLK4 turnover → STIL → SAS6 cartwheel → CPAP/CEP135 → elongation → CP110 → daughter maturation → disengagement/licensing → amplification → cilia/development → evidence/model limits.
Begin with:
“How does a cell build exactly one ninefold-symmetric daughter centriole without copying from a DNA template?”
Connect This to the eduKate Learning Estate
- Cell Cycle and Checkpoints
- Cytoskeleton and Molecular Motors
- Cilia, Flagella and Cell Motility
- Intraflagellar Transport and Cilia
These remain broader or adjacent canonical owners. This article owns PLK4–STIL–SAS6-mediated centriole duplication and number control.
Research Foundations and Further Learning
- 2025 Cytoskeleton: PLK4 as the master regulator of centriole duplication.
- 2025 Molecular Biology of the Cell: CEP152 binding stimulates PLK4 activation.
- 2024 ultrastructure-expansion microscopy mapping of human procentriole assembly.
- Foundational PLK4–STIL phosphorylation studies defining SAS6 recruitment.
- Structural work on SAS6 cartwheel assembly and ninefold symmetry.
- 2026 Journal of Biological Chemistry: FBXW7-dependent control of PLK4-phosphorylated STIL–SAS6 assemblies.
The Quiet Ending
The beginner asks: “Why does a cell need centrioles?”
The developing cell biologist asks: “How does one site around the parent centriole become the daughter-building site?”
The advanced learner asks: “How can PLK4 be strong enough to initiate duplication yet self-destruct fast enough to prevent extra daughters?”
And the professional asks:
Can we close one centriole-duplication event from PLK4 spatial symmetry breaking through cartwheel assembly and wall growth to a single correctly licensed daughter strongly enough to explain why there was exactly one copy rather than zero or several?
