CFAP20

gene
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Also known as GTL3fSAP23

Summary

CFAP20 (cilia and flagella associated protein 20, HGNC:29523) is a protein-coding gene on chromosome 16q21, encoding Cilia- and flagella-associated protein 20 (Q9Y6A4). Cilium- and flagellum-specific protein that plays a role in axonemal structure organization and motility. It is a selective cancer dependency (DepMap: 67.2% of cell lines).

Enables RNA binding activity. Involved in several processes, including positive regulation of feeding behavior; protein polyglutamylation; and regulation of cilium beat frequency involved in ciliary motility. Located in microtubule cytoskeleton and nucleoplasm.

Source: NCBI Gene 29105 — RefSeq curated summary.

At a glance

  • GWAS associations: 1
  • Clinical variants (ClinVar): 26 total — 5 likely-pathogenic
  • Druggable target: yes — 1 molecules with ChEMBL bioactivity
  • Cancer dependency (DepMap): dependent in 67.2% of screened cell lines
  • MANE Select transcript: NM_013242

Identifiers

Gene identifiers

FieldValue
HGNC IDHGNC:29523
Approved symbolCFAP20
Namecilia and flagella associated protein 20
Location16q21
Locus typegene with protein product
StatusApproved
AliasesGTL3, fSAP23
Ensembl geneENSG00000070761
Ensembl biotypeprotein_coding
OMIM617906
Entrez29105

Gene structure

Transcript identifiers

Ensembl transcripts: 11 — 6 protein_coding, 4 retained_intron, 1 protein_coding_CDS_not_defined

ENST00000262498, ENST00000562443, ENST00000562622, ENST00000564150, ENST00000565880, ENST00000567092, ENST00000567660, ENST00000896541, ENST00000933126, ENST00000933127, ENST00000933128

RefSeq mRNA: 1 — MANE Select: NM_013242 NM_013242

CCDS: CCDS10793

Canonical transcript exons

ENST00000262498 — 6 exons

ExonStartEnd
ENSE000006864455811526958115457
ENSE000009210885811359258114030
ENSE000011008135812903258129381
ENSE000035237945811604158116152
ENSE000036167175811481058114920
ENSE000036740105811687258116951

Expression profiles

Bgee: expression breadth ubiquitous, 288 present calls, max score 98.09.

FANTOM5 (CAGE): breadth ubiquitous, TPM avg 32.9700 / max 200.2936, expressed in 1817 samples.

FANTOM5 promoters (6 alternative TSS)

Promoter IDTPM avgSamples expressed
15760120.80071803
15760210.31991779
1576031.2948883
1576000.3090121
1575990.210976
1575960.03466

Top tissues by expression

293 total, by Bgee expression score (0-100, higher = more expressed):

TissueAnatomy IDExpression scoreQuality
bronchial epithelial cellCL:000232898.09gold quality
spermCL:000001997.15gold quality
epithelium of bronchusUBERON:000203196.98gold quality
ventricular zoneUBERON:000305396.73gold quality
adult organismUBERON:000702396.64gold quality
bronchusUBERON:000218596.49gold quality
endothelial cellCL:000011596.03gold quality
cortical plateUBERON:000534395.92gold quality
left testisUBERON:000453395.87gold quality
ganglionic eminenceUBERON:000402395.81gold quality
middle temporal gyrusUBERON:000277195.61gold quality
right testisUBERON:000453495.55gold quality
embryoUBERON:000092295.41gold quality
male germ cellCL:000001595.33gold quality
calcaneal tendonUBERON:000370195.29gold quality
right uterine tubeUBERON:000130295.16gold quality
upper leg skinUBERON:000426295.11gold quality
testisUBERON:000047394.86gold quality
prefrontal cortexUBERON:000045194.76gold quality
pigmented layer of retinaUBERON:000178294.59gold quality
retinaUBERON:000096694.56gold quality
Brodmann (1909) area 23UBERON:001355494.19gold quality
pituitary glandUBERON:000000794.11gold quality
adenohypophysisUBERON:000219694.05gold quality
caput epididymisUBERON:000435894.04gold quality
skin of hipUBERON:000155493.89gold quality
epithelium of nasopharynxUBERON:000195193.89gold quality
metanephric glomerulusUBERON:000473693.74gold quality
left ventricle myocardiumUBERON:000656693.50gold quality
frontal cortexUBERON:000187093.39gold quality

Single-cell (SCXA)

Detected in 3 experiment(s), a significant marker in 2.

ExperimentMarker?Max mean expression
E-GEOD-81547yes11.89
E-CURD-89no1104.20
E-ANND-3no0.00

Regulation

Is transcription factor: no

Upstream regulators (CollecTRI, top): E2F4, RELA, TADA2A, TBP

miRNA regulators (miRDB)

39 targeting CFAP20, top 30 by miRDB confidence (max_score; target_count = how many genes the miRNA targets in total — lower means more specific):

miRNAMax scoreAvg scoremiRNA target_count
HSA-MIR-3163100.0077.238605
HSA-MIR-1277-5P100.0073.955056
HSA-MIR-5011-5P100.0083.465820
HSA-MIR-5692B100.0071.322622
HSA-MIR-5692C100.0071.322622
HSA-MIR-513A-5P100.0069.772465
HSA-MIR-520D-5P99.9873.344883
HSA-MIR-524-5P99.9873.434882
HSA-MIR-9983-3P99.9471.483631
HSA-MIR-6753-3P99.9366.57637
HSA-MIR-7107-3P99.9366.73627
HSA-MIR-129-5P99.8870.263273
HSA-MIR-3180-5P99.8269.122422
HSA-MIR-4760-5P99.8069.881619
HSA-MIR-57799.7869.132479
HSA-MIR-3680-3P99.7572.513095
HSA-MIR-452799.6667.43714
HSA-MIR-6848-3P99.6466.49885
HSA-MIR-6503-5P99.6266.96597
HSA-MIR-425-5P99.5967.67900
HSA-MIR-1212399.5271.792990
HSA-MIR-5571-5P99.4966.991764
HSA-MIR-120699.3069.321016
HSA-MIR-488-5P99.2868.12821
HSA-MIR-410-3P99.2769.982457
HSA-MIR-6843-3P99.2666.42915
HSA-MIR-664A-3P99.2271.082696
HSA-MIR-122B-3P99.2168.901333
HSA-MIR-21-3P99.2168.951312
HSA-MIR-6792-3P98.4166.861359

Functional genomics

DepMap (CRISPR cell-line fitness): dependent in 67.2% of screened cell lines.

Cross-species orthologs

5 orthologs

OrganismSymbolGene ID
danio_reriocfap20ENSDARG00000100514
mus_musculusCfap20ENSMUSG00000031796
rattus_norvegicusCfap20ENSRNOG00000042179
drosophila_melanogasterBug22FBGN0032248
caenorhabditis_elegansWBGENE00008288

Paralogs (1): CFAP20DC (ENSG00000163689)

Protein

Protein identifiers

Cilia- and flagella-associated protein 20Q9Y6A4 (reviewed: Q9Y6A4)

Alternative names: Basal body up-regulated protein 22, Transcription factor IIB

All UniProt accessions (2): Q9Y6A4, H3BPA3

UniProt curated annotations — full annotation on UniProt →

Function. Cilium- and flagellum-specific protein that plays a role in axonemal structure organization and motility. Microtubule inner protein (MIP) part of the dynein-decorated doublet microtubules (DMTs) in cilia axoneme, which is required for motile cilia beating. Involved in the regulation of the size and morphology of cilia. Required for axonemal microtubules polyglutamylation.

Subunit / interactions. Microtubule inner protein component of sperm flagellar doublet microtubules. Interacts with CFAP65.

Subcellular location. Nucleus. Cytoplasm. Cytoskeleton. Microtubule organizing center. Centrosome. Centriole. Cilium basal body. Cilium axoneme. Flagellum axoneme.

Similarity. Belongs to the CFAP20 family.

RefSeq proteins (1): NP_037374* (*=MANE)

Domains & families (InterPro)

IDNameType
IPR007714CFA20_domDomain
IPR040441CFA20/CFAP20DCFamily

Pfam: PF05018

UniProt features (1 total): chain 1

Structure

Experimental structures (PDB)

2 structures.

PDBMethodResolution (Å)
7UNGELECTRON MICROSCOPY3.6
8J07ELECTRON MICROSCOPY4.1

Predicted structure (AlphaFold)

ModelpLDDTFraction very-high
AF-Q9Y6A4-F191.810.83

Function

Pathways and Gene Ontology

Reactome pathways

0 pathways

MSigDB gene sets: 188 (showing top): GOBP_BEHAVIOR, GOBP_REGULATION_OF_MICROTUBULE_BASED_PROCESS, CMYB_01, RACCACAR_AML_Q6, GOBP_POSITIVE_REGULATION_OF_BEHAVIOR, GOCC_MICROTUBULE_ORGANIZING_CENTER, WEI_MYCN_TARGETS_WITH_E_BOX, PAX8_B, GOBP_REGULATION_OF_BEHAVIOR, GOBP_REGULATION_OF_FEEDING_BEHAVIOR, AML_Q6, GOBP_CILIUM_ORGANIZATION, GOBP_CILIUM_MOVEMENT, GOBP_REGULATION_OF_MICROTUBULE_BASED_MOVEMENT, GOBP_CILIUM_OR_FLAGELLUM_DEPENDENT_CELL_MOTILITY

GO Biological Process (6): protein polyglutamylation (GO:0018095), flagellated sperm motility (GO:0030317), cilium assembly (GO:0060271), regulation of cilium beat frequency involved in ciliary motility (GO:0060296), positive regulation of cell motility (GO:2000147), positive regulation of feeding behavior (GO:2000253)

GO Molecular Function (2): RNA binding (GO:0003723), protein binding (GO:0005515)

GO Cellular Component (15): nucleoplasm (GO:0005654), centriole (GO:0005814), axonemal microtubule (GO:0005879), cilium (GO:0005929), motile cilium (GO:0031514), ciliary basal body (GO:0036064), sperm flagellum (GO:0036126), extracellular exosome (GO:0070062), sperm principal piece (GO:0097228), axonemal B tubule inner sheath (GO:0160112), nucleus (GO:0005634), cytoplasm (GO:0005737), cytoskeleton (GO:0005856), microtubule (GO:0005874), cell projection (GO:0042995)

GO top-level categories

Rollup of top GO terms by namespace:

CategoryTerms
cellular anatomical structure5
microtubule organizing center2
intracellular membraneless organelle2
cilium2
peptidyl-glutamic acid modification1
cilium-dependent cell motility1
cilium movement involved in cell motility1
sperm motility1
axoneme assembly1
intraciliary transport involved in cilium assembly1
cilium organization1
protein localization to cilium1
organelle assembly1
trans-Golgi to periciliary membrane compartment transport1
plasma membrane bounded cell projection assembly1
ciliary transition zone assembly1
regulation of cilium beat frequency1
regulation of cilium movement involved in cell motility1
regulation of biological quality1
positive regulation of locomotion1
positive regulation of cellular process1
cell motility1
regulation of cell motility1
feeding behavior1
positive regulation of behavior1
regulation of feeding behavior1
nucleic acid binding1
binding1
nuclear lumen1
cytoplasmic microtubule1
axoneme1
intraciliary transport particle1
membrane-bounded organelle1
plasma membrane bounded cell projection1
9+2 motile cilium1
extracellular vesicle1
sperm flagellum1
A axonemal microtubule1
axonemal microtubule doublet inner sheath1
intracellular membrane-bounded organelle1

Protein interactions and networks

STRING

1535 interactions, top by confidence (×1000):

Protein AProtein BPartner UniProtScore
CFAP20TBPP20226912
CFAP20GTF2BQ00403880
CFAP20DRAP1Q14919804
CFAP20DR1Q01658702
CFAP20TBC1D32Q96NH3528
CFAP20RELQ04864481
CFAP20FAHD2AQ96GK7468
CFAP20H2BC21Q16778461
CFAP20H2AC19P20670458
CFAP20H2AC20Q16777458
CFAP20RELAQ04206443
CFAP20HNF4AP41235428
CFAP20CFAP298P57076425
CFAP20TMEM17Q86X19422
CFAP20CEP41Q9BYV8403

IntAct

73 interactions, top by confidence:

ABTypeScore
PLK1SPAG9psi-mi:“MI:0914”(association)0.790
CLASRPCFAP20psi-mi:“MI:0915”(physical association)0.790
ARL2BPCFAP20psi-mi:“MI:0915”(physical association)0.790
FOXJ1RFX3psi-mi:“MI:0914”(association)0.730
LUC7L2ZRANB2psi-mi:“MI:0914”(association)0.640
CFAP20SFSWAPpsi-mi:“MI:0914”(association)0.620
SFSWAPCFAP20psi-mi:“MI:0915”(physical association)0.620
CFAP20YWHAGpsi-mi:“MI:0915”(physical association)0.590
CFAP20LRRK2psi-mi:“MI:0407”(direct interaction)0.590
CFAP20KPNA4psi-mi:“MI:0914”(association)0.510
PRPF38AH2BC17psi-mi:“MI:0914”(association)0.510
SF3A2CFAP20psi-mi:“MI:0915”(physical association)0.400
CFAP20TFCP2L1psi-mi:“MI:0915”(physical association)0.370
Pqbp1PRPF4psi-mi:“MI:0914”(association)0.350
Kif19psi-mi:“MI:0914”(association)0.350
FOXJ1ACSL4psi-mi:“MI:0914”(association)0.350
JUNpsi-mi:“MI:0914”(association)0.350
JUNTPM3psi-mi:“MI:0914”(association)0.350
Xpo1IFT56psi-mi:“MI:0914”(association)0.350
ESR1ESYT2psi-mi:“MI:0914”(association)0.350
LRRK2psi-mi:“MI:0914”(association)0.350
CFAP20PRPF40Apsi-mi:“MI:0914”(association)0.350
ENGIGKV2-28psi-mi:“MI:0914”(association)0.350
CLK3AIPpsi-mi:“MI:0914”(association)0.350
DYRK2ZSWIM8psi-mi:“MI:0914”(association)0.350
CEP135MCRIP1psi-mi:“MI:0914”(association)0.350
CEP135WWP2psi-mi:“MI:0914”(association)0.350
CEP135WDR91psi-mi:“MI:0914”(association)0.350

BioGRID (129): CFAP20 (Affinity Capture-MS), CFAP20 (Affinity Capture-MS), CFAP20 (Affinity Capture-MS), CFAP20 (Affinity Capture-MS), CFAP20 (Affinity Capture-MS), CFAP20 (Affinity Capture-MS), SFSWAP (Affinity Capture-MS), CLASRP (Affinity Capture-MS), U2AF1 (Affinity Capture-MS), SFSWAP (Affinity Capture-MS), TBC1D32 (Affinity Capture-MS), CDK20 (Affinity Capture-MS), ARL2BP (Affinity Capture-MS), CLASRP (Affinity Capture-MS), RABEPK (Affinity Capture-MS)

ESM2 similar proteins: A0A1S4A695, A0CDD4, A2VE01, A8IU92, B0R0D7, D3ZRP6, O88958, O97556, P46926, P48454, P50397, P50399, P62495, P62496, P62497, P62498, Q0VCX5, Q1W377, Q24208, Q259G4, Q3SYW1, Q499T7, Q4R7R3, Q503E1, Q5PQL4, Q5R4C7, Q5R8T8, Q5U2Q7, Q5ZHP3, Q5ZJL4, Q61598, Q64422, Q6B857, Q6GL74, Q6GPY6, Q6PBJ2, Q6Q7J2, Q7XPW5, Q8BTU1, Q8BWY3

Diamond homologs: A0CDD4, A8IU92, Q499T7, Q5ZHP3, Q61JK7, Q6B857, Q6GL74, Q6GPY6, Q6PBJ2, Q86D25, Q8BTU1, Q9VKV8, Q9Y6A4

SIGNOR signaling

0 interactions.

Enriched among interaction partners

Reactome pathways and GO biological processes over-represented among this gene’s 72 IntAct physical interaction partners (hypergeometric vs the genome-wide background, BH-FDR, gene-set size 15–500, ranked by fold). A functional readout of the neighbourhood — distinct from this gene’s own memberships above, and biased toward well-studied / hub proteins, so read it as themes rather than proof.

Reactome pathways:

PathwayPartnersFoldFDR
mRNA Polyadenylation610.8×3e-03
mRNA Splicing - Major Pathway88.9×9e-04

GO biological processes:

GO termPartnersFoldFDR
mRNA splicing, via spliceosome811.1×4e-04

Disease & clinical

Clinical variants and AI predictions

ClinVar

26 variants total. Per-class counts are floors (≥ shown; pagination cap):

ClassificationCount (floor)
Pathogenic0
Likely pathogenic5
Uncertain significance17
Likely benign0
Benign0

Top pathogenic / likely-pathogenic (5)

Variant IDHGVSClassification
1701087NM_013242.3(CFAP20):c.305G>A (p.Arg102His)Likely pathogenic
1701088NM_013242.3(CFAP20):c.257A>G (p.Tyr86Cys)Likely pathogenic
1701089NM_013242.3(CFAP20):c.397del (p.Gln133fs)Likely pathogenic
1701090NM_013242.3(CFAP20):c.164+1G>ALikely pathogenic
1701091NM_013242.3(CFAP20):c.457A>G (p.Arg153Gly)Likely pathogenic

SpliceAI

610 predictions. Top by Δscore:

VariantEffectΔscore
16:58114028:TTG:Tacceptor_gain1.0000
16:58115263:CAGTA:Cdonor_loss1.0000
16:58115264:AGTAC:Adonor_loss1.0000
16:58115265:GTACC:Gdonor_loss1.0000
16:58115266:TA:Tdonor_loss1.0000
16:58115267:A:Cdonor_loss1.0000
16:58115268:C:CAdonor_loss1.0000
16:58115268:CCT:Cdonor_gain1.0000
16:58115270:TGC:Tdonor_gain1.0000
16:58115271:G:Adonor_gain1.0000
16:58115453:AGTAC:Aacceptor_gain1.0000
16:58115454:GTAC:Gacceptor_gain1.0000
16:58115455:TAC:Tacceptor_gain1.0000
16:58115456:AC:Aacceptor_gain1.0000
16:58115457:CC:Cacceptor_gain1.0000
16:58115458:C:CAacceptor_loss1.0000
16:58115458:C:CCacceptor_gain1.0000
16:58115458:C:Tacceptor_gain1.0000
16:58115459:T:Aacceptor_loss1.0000
16:58115460:G:Cacceptor_gain1.0000
16:58115460:G:GCacceptor_gain1.0000
16:58115465:A:ACacceptor_gain1.0000
16:58115465:A:Cacceptor_gain1.0000
16:58115468:C:CTacceptor_gain1.0000
16:58116038:TACC:Tdonor_loss1.0000
16:58116039:A:ACdonor_gain1.0000
16:58116039:AC:Adonor_gain1.0000
16:58116039:ACCTG:Adonor_gain1.0000
16:58116040:C:CGdonor_gain1.0000
16:58116040:CC:Cdonor_gain1.0000

AlphaMissense

1276 scored. Top likely-pathogenic:

VariantProtein changeam_pathogenicity
16:58115347:C:AW129C1.000
16:58115347:C:GW129C1.000
16:58115349:A:GW129R1.000
16:58115349:A:TW129R1.000
16:58115426:A:GF103S1.000
16:58129043:A:GW25R1.000
16:58129043:A:TW25R1.000
16:58114895:C:GR164P0.999
16:58114904:C:GR161P0.999
16:58115348:C:GW129S0.999
16:58115369:G:TP122H0.999
16:58115377:G:CC119W0.999
16:58115378:C:TC119Y0.999
16:58115416:A:CS106R0.999
16:58115416:A:TS106R0.999
16:58115417:C:AS106I0.999
16:58115418:T:GS106R0.999
16:58115423:C:GR104P0.999
16:58115432:C:GR101P0.999
16:58115433:G:TR101S0.999
16:58116885:C:AG51W0.999
16:58116885:C:GG51R0.999
16:58116885:C:TG51R0.999
16:58129068:G:CS16R0.999
16:58129068:G:TS16R0.999
16:58129070:T:GS16R0.999
16:58114856:A:GL177P0.998
16:58114892:A:TV165D0.998
16:58114898:C:GR163P0.998
16:58114913:G:TA158E0.998

dbSNP variants (sampled 300 via entrez): RS1000101082 (16:58123622 A>C), RS1000358958 (16:58119848 C>A), RS1000360398 (16:58123738 T>C), RS1000453905 (16:58123403 T>C), RS1000460580 (16:58113463 T>C), RS1000529050 (16:58126895 T>C,G), RS1000582756 (16:58119458 A>G), RS1000811652 (16:58126570 A>C), RS1001364229 (16:58125440 T>C), RS1001483907 (16:58119297 G>A), RS1001537450 (16:58131104 C>T), RS1001572566 (16:58118683 G>T), RS1001668848 (16:58118730 G>A), RS1001701552 (16:58118934 C>T), RS1002464647 (16:58126303 G>T)

Disease associations

OMIM: gene MIM:617906 | disease phenotypes:

GenCC curated gene-disease

Mondo (0):

Orphanet (0):

HPO phenotypes

0 total (0 of 0 shown, HPO-id order):

GWAS associations

1 associations (top):

StudyTraitp-value
GCST005790_39Rosacea symptom severity2.000000e-06

EFO canonical traits (1, from GWAS)

EFO IDTrait name
EFO:0009180rosacea severity measurement

Drugs & pharmacology

Drug and pharmacology data

Is drug target: yes

ChEMBL targets (1): CHEMBL5724749 (SINGLE PROTEIN)

Molecules with ChEMBL bioactivity

1 molecules (phase ≥1), by development phase (incl. off-target/promiscuous compounds). Patent mentions across the top 20 by phase: 1,538 (via chembl_molecule»patent_compound — counts attach to the compound, not the gene–compound relationship, so off-target/promiscuous molecules can dominate).

MoleculeNamePhasePatents
CHEMBL1232461MOLIBRESIB21,538

PharmGKB: 1 entry (VIP=true, CPIC=false)

ChEMBL bioactivities

2 potent at pChembl≥5 of 2 total, top 2 by pChembl (potency: 10 = 0.1 nM, 6 = 1 µM).

pChemblTypeValueUnitMolecule
7.38Kd42nMMOLIBRESIB
7.10IC5080nMMOLIBRESIB

PubChem BioAssay actives

2 with measured affinity, of 7 total; 1 most potent distinct compounds. Largely complementary to BindingDB; screening values are coarse (µM, 4 dp), so sub-nM hits tie at the floor.

CompoundAssayTypeValueUnit
2-[(4S)-6-(4-chlorophenyl)-8-methoxy-1-methyl-4H-[1,2,4]triazolo[4,3-a][1,4]benzodiazepin-4-yl]-N-ethylacetamide2179219: Binding affinity against C16ORF80 (unknown origin) assessed as apparent dissociation constant incubated for 1 hr by colloidal coomassie staining based LC-MS/MS analysiskd0.0420uM

CTD chemical–gene interactions

28 total (human), top 28 by PubMed support.

ChemicalActions (top 5)PubMed papers
Acetaminophenincreases expression, affects response to substance3
Smokedecreases expression, increases abundance, increases expression3
sodium arseniteaffects expression, increases expression2
Air Pollutantsdecreases expression, increases abundance, increases expression2
bisphenol Aaffects cotreatment, increases methylation1
2-methyl-4-isothiazolin-3-oneincreases expression1
arseniteaffects binding, increases reaction1
butyraldehydeincreases expression1
di-n-butylphosphoric acidaffects expression1
abrineincreases expression1
licochalcone Bincreases expression1
Fulvestrantaffects cotreatment, increases methylation1
Air Pollutants, Occupationalincreases expression1
Cisplatinincreases expression1
Coumestrolincreases expression1
Dimethyl Sulfoxideincreases expression1
Doxorubicinincreases expression1
Methyl Methanesulfonateincreases expression1
Nickelincreases expression1
Thiramincreases expression1
Tobacco Smoke Pollutiondecreases expression1
Tretinoindecreases expression1
Urethaneincreases expression1
Valproic Acidincreases expression1
Cyclosporinedecreases expression1
Copper Sulfatedecreases expression1
Vitamin K 3affects expression1
Particulate Matterincreases abundance, decreases expression1

ChEMBL screening assays

7 unique, capped per target: 7 binding

Representative assays (with source publication via chembl_document):

Assay IDTypeDescriptionSource paper
CHEMBL5697589BindingInhibition of C16ORF80 (unknown origin) assessed as fold change at 10 uM incubated for 1 hr by colloidal coomassie staining based LC-MS/MS analysisInhibition of BET recruitment to chromatin as an effective treatment for MLL-fusion leukaemia. — Nature

Clinical trials (associated diseases)

0 trials via MONDO — disease-level, not drug-specific.

No linked Atlas pages yet — the cross-entity mesh grows as the corpus expands.