tp53bp2b is one of two zebrafish co-orthologs of human TP53BP2 (ASPP2), a large cytoplasmic scaffold protein with an N-terminal Ras-associating (ubiquitin-like) domain, a coiled-coil and a long proline-rich, largely disordered middle region, and a C-terminal module of four ankyrin repeats and an SH3 domain. In mammals this C-terminal module binds the p53 DNA-binding domain and enhances p53-dependent apoptosis, and ASPP2 also acts at apical cell junctions, where it binds Par-3 and scaffolds PP1 and YAP. In zebrafish embryos, Aspp2b (like its paralog Aspp2a) binds Irs-1 and restrains embryonic body growth without changing developmental rate, by dampening Akt signaling. tp53bp2b transcripts are maternally provided and present in early embryos, are low during gastrulation and organogenesis, and are found in many larval and adult tissues. A GFP-tagged form expressed in embryos is cytoplasmic, and tp53bp2b is induced by the ciliogenic transcription factor Foxj1.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0002039 p53 binding | IBA GO_REF:0000033 | ACCEPT | Summary: p53 binding propagated from the PANTHER ASPP node (human ASPP2 and worm ape-1 donors). Reason: The p53-binding module of ASPP2 is the C-terminal ankyrin repeats plus SH3 domain. The four ankyrin repeats of tp53bp2b are 90.7-97.1% identical to human TP53BP2 and the SH3 domain is intact, so tp53bp2b sits inside the clade that inherited this function with no sign of loss. Binding of zebrafish Aspp2b to Tp53 has not itself been tested. Supporting Evidence: PMID:8875926 the SH3 domain binds the L3 loop of p53 in a manner distinct from that of previously characterized SH3-polyproline peptide complexes, and (ii) an ankyrin repeat, which forms an L-shaped structure consisting of a beta hairpin and two alpha helices, binds the L2 loop of p53 file:DANRE/tp53bp2a/tp53bp2a-bioinformatics/RESULTS.md The four ankyrin repeats are 90.6-100% identical to human TP53BP2 in both copies |
| GO:0002039 p53 binding | IEA GO_REF:0000002 | ACCEPT | Summary: p53 binding from the InterPro ASPP1/2 family signature. Reason: Same claim as the IBA row, reached from the ASPP1/2 family signature; consistent with the conserved ankyrin-SH3 module. Supporting Evidence: PMID:11684014 ASPP proteins interact with p53 and specifically enhance p53-induced apoptosis but not cell cycle arrest. |
| GO:0003341 cilium movement | IMP PMID:25139857 Systematic discovery of novel ciliary genes through function... | UNDECIDED | Summary: From a morpholino screen of 50 randomly chosen Foxj1-induced genes, scored for motile-cilia phenotypes and, for ten genes, for Kupffer's vesicle cilia motility. Reason: tp53bp2b is not named in the main text of the paper; its per-gene data are in supplementary Table S3, which is not in the cache, so I cannot see which phenotypes or motility values were recorded for it. The evidence is a single splice-blocking morpholino with no mutant, and no ciliary role is known for ASPP2 in other species. The paper itself notes that most Foxj1 targets are not ciliary proteins and may act indirectly. I defer to the curator but cannot confirm. Supporting Evidence: PMID:25139857 However, upon morpholino-mediated knockdown of nine out of the ten selected genes, the percentage of motile cilia decreased to as low as 2% PMID:25139857 Therefore, it is likely that most of the FIGs encode novel membrane, cytoplasmic or nuclear regulators of cilia formation and function. |
| GO:0005634 nucleus | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Nuclear activity propagated from human ASPP2 and ASPP1. Reason: Mammalian ASPP proteins act on p53 at pro-apoptotic promoters, so a nuclear pool is plausible, but the best-characterized sites of ASPP2 are cytoplasmic and junctional, and GFP-tagged Aspp2b was scored as cytoplasmic in zebrafish embryos. Kept as a non-core location. Supporting Evidence: PMID:11684014 ASPP enhance the DNA binding and transactivation function of p53 on the promoters of proapoptotic genes in vivo. |
| GO:0005634 nucleus | IEA GO_REF:0000044 | KEEP AS NON CORE | Summary: Nucleus from the UniProt subcellular-location rule (ARBA). Reason: As for the IBA row; a minor location for this largely cytoplasmic and junctional scaffold. Supporting Evidence: PMID:11684014 ASPP enhance the DNA binding and transactivation function of p53 on the promoters of proapoptotic genes in vivo. |
| GO:0005737 cytoplasm | IDA PMID:25139857 Systematic discovery of novel ciliary genes through function... | ACCEPT | Summary: GFP-tagged Aspp2b expressed from injected mRNA in zebrafish embryos localized to the cytoplasm (not to cilia). Reason: Direct localization of the zebrafish protein, consistent with mammalian ASPP2 being a cytoplasmic and junctional scaffold. Per-gene images are in the supplement; the main text describes the non-ciliary class of proteins as cytoplasmic, nuclear or membrane. Supporting Evidence: PMID:25139857 Surprisingly, the remaining proteins showed no association with ciliary structures |
| GO:0005737 cytoplasm | IEA GO_REF:0000044 | ACCEPT | Summary: Cytoplasm from the UniProt subcellular-location rule (ARBA). Reason: Agrees with the IDA row and with mammalian ASPP2. Supporting Evidence: PMID:25360797 Here we report that the tumour suppressor ASPP2 forms an apical-lateral polarity complex at the level of tight junctions in polarised epithelial cells |
| GO:0005912 adherens junction | IBA GO_REF:0000033 | ACCEPT | Summary: Adherens junction propagated from Drosophila ASPP. Reason: Junctional localization is a conserved property of ASPP2 (mouse ASPP2 maintains tight/adherens junctions and binds Par-3) and of fly ASPP. tp53bp2b keeps the domains; no zebrafish junction data. Supporting Evidence: PMID:20619750 Mechanistically, ASPP2 maintains the integrity of tight/adherens junctions. |
| GO:0007165 signal transduction | IEA GO_REF:0000002 | MODIFY | Summary: Generic signal transduction from the Ras-associating domain InterPro2GO mapping. Reason: Not wrong but uninformative. The zebrafish experiment on this gene shows it dampens Akt signaling downstream of Irs-1, which is captured by the more specific term already carried by experimental evidence. Proposed replacements: negative regulation of phosphatidylinositol 3-kinase/protein kinase B signal transduction Supporting Evidence: PMID:24362258 Aspp2a and 2b inhibit Akt signaling. This inhibition was reversed by coinjection of myr-Akt1, a constitutively active form of Akt1. |
| GO:0042981 regulation of apoptotic process | IEA GO_REF:0000002 | ACCEPT | Summary: Regulation of apoptosis from the ASPP1/2 family signature. Reason: Regulation of p53-dependent apoptosis is the defining function of the ASPP family. It is untested for zebrafish Aspp2b, but the p53-binding module is conserved. The broad term is acceptable for an IEA. Supporting Evidence: PMID:11684014 Inhibition of endogenous ASPP function suppresses the apoptotic function of endogenous p53 in response to apoptotic stimuli. |
| GO:0043009 chordate embryonic development | IMP PMID:24362258 Aspp2 negatively regulates body growth but not developmental... | MODIFY | Summary: Knockdown of aspp2b altered embryonic growth in zebrafish. Reason: The paper's finding is specific: Aspp2b restrains body growth while developmental rate (timing) is unchanged. "Chordate embryonic development" is broad and implies a developmental-timing role the authors explicitly exclude. Negative regulation of multicellular organism growth states the claim. I have only the abstract; the refinement follows the title and abstract, not a disagreement with the curator. Proposed replacements: negative regulation of multicellular organism growth Supporting Evidence: PMID:24362258 Here, we show that zebrafish Aspp2a and Aspp2b negatively regulate embryonic growth without affecting developmental rate. |
| GO:0048471 perinuclear region of cytoplasm | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Perinuclear cytoplasm propagated from rat Tp53bp2. Reason: Consistent with a cytoplasmic protein; not a site of any characterized function and not tested in zebrafish. The best-characterized ASPP2 site is the apical junction. Supporting Evidence: PMID:25360797 Here we report that the tumour suppressor ASPP2 forms an apical-lateral polarity complex at the level of tight junctions in polarised epithelial cells |
| GO:0051898 negative regulation of phosphatidylinositol 3-kinase/protein kinase B signal transduction | IMP PMID:24362258 Aspp2 negatively regulates body growth but not developmental... | ACCEPT | Summary: Aspp2b inhibits Akt signaling in zebrafish embryos; the effect is reversed by constitutively active Akt1. Reason: Direct zebrafish evidence on this copy, with an epistasis test (myr-Akt1) and a mechanism (binding to Irs-1). Abstract only in cache; accepted, deferring to the curator who read the full text. Supporting Evidence: PMID:24362258 Aspp2a and 2b inhibit Akt signaling. This inhibition was reversed by coinjection of myr-Akt1, a constitutively active form of Akt1. PMID:24362258 Zebrafish Aspp2a and Aspp2b physically bound with Irs-1, and the growth inhibitory effects of ASPP2/Aspp2 depend on the presence of their ankyrin repeats and SH3 domains. |
| GO:0072332 intrinsic apoptotic signaling pathway by p53 class mediator | IBA GO_REF:0000033 | ACCEPT | Summary: p53-mediated intrinsic apoptosis, propagated from human ASPP2 and ASPP1. Reason: This is the ancestral ASPP function, and the p53-binding module is conserved in tp53bp2b. Not yet tested in zebrafish. Supporting Evidence: PMID:11684014 ASPP enhance the DNA binding and transactivation function of p53 on the promoters of proapoptotic genes in vivo. |
| GO:0043560 insulin receptor substrate binding | IPI PMID:24362258 Aspp2 negatively regulates body growth but not developmental... | NEW | Summary: Zebrafish Aspp2b binds Irs-1. Reason: Physical interaction with Irs-1 reported for both zebrafish copies, and the growth phenotype needs the ankyrin-SH3 module; this is the only molecular interaction shown for the zebrafish protein and it explains the Akt phenotype. Abstract only; assay details not visible. Supporting Evidence: PMID:24362258 Zebrafish Aspp2a and Aspp2b physically bound with Irs-1, and the growth inhibitory effects of ASPP2/Aspp2 depend on the presence of their ankyrin repeats and SH3 domains. |
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Download this section (compressed HTML)Q: Does tp53bp2b have a real role in motile cilia (as the morpholino screen suggested), and would a stable mutant confirm it?
Q: Both copies are maternally provided, but only tp53bp2b drops to near background during gastrulation and organogenesis. Is that a loss of zygotic enhancers in tp53bp2b, and does the gar gene show continuous expression?
Q: Does Aspp2b bind Tp53 and enhance p53-dependent apoptosis?
Experiment: Make a stable tp53bp2b mutant (and maternal-zygotic mutant, given maternal expression); score Kupffer's vesicle cilia motility, left-right asymmetry markers and kidney cysts.
Hypothesis: tp53bp2b is required for Kupffer's vesicle cilia motility.
Type: loss of function
Experiment: Rescue the growth phenotype of each single or double mutant with either coding sequence.
Hypothesis: The Aspp2a and Aspp2b proteins are interchangeable.
Type: cross-rescue
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