mapre3b (microtubule-associated protein, RP/EB family, member 3b) is one of two zebrafish co-orthologs of vertebrate MAPRE3 (end-binding protein 3, EB3), retained from the teleost genome duplication; its paralog is mapre3a. It encodes a microtubule plus-end tracking protein (+TIP) with an N-terminal calponin-homology (CH) domain that binds growing microtubule ends, a flexible linker, a C-terminal EB-homology coiled-coil domain that mediates dimerization and binding of partner +TIPs, and an acidic tail ending in an aromatic residue. In mammals EB3 is enriched in neurons, tracks growing microtubule ends and, with EB1, promotes persistent microtubule growth by suppressing catastrophes. The zebrafish protein keeps all of these features. mapre3b transcripts are maternally supplied and present at every embryonic stage, and adult RNA-seq detects it broadly (brain, retina, muscle, heart, gill, intestine, liver and other tissues). No functional study of the zebrafish gene has been published.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005815 microtubule organizing center | IBA GO_REF:0000033 | ACCEPT | Summary: Microtubule organizing center (IBA) from the RP/EB family node PTN000065701. Reason: EB proteins concentrate at centrosomes and the Golgi-associated MTOC as well as at plus ends; UniProt's family-level function text for mapre3b notes anchoring of microtubules at centrosomes. mapre3b keeps every conserved EB domain, so it is inside the clade that inherited this localization. Non-core location; no zebrafish data. Same call for mapre3a. Supporting Evidence: PMID:19255245 End binding proteins (EBs) are highly conserved core components of microtubule plus-end tracking protein networks. file:DANRE/mapre3a/mapre3a-bioinformatics/RESULTS.md Both copies keep the microtubule-binding CH domain, the EBH dimerization/partner-binding domain and the C-terminal aromatic tail. |
| GO:0005856 cytoskeleton | IEA GO_REF:0000044 | ACCEPT | Summary: Cytoskeleton, from the UniProt 'Cytoplasm, cytoskeleton' subcellular location (ARBA rule). Reason: Correct but general; the protein decorates microtubules. The more specific microtubule plus-end and cytoplasmic microtubule rows carry the informative location. Supporting Evidence: PMID:10644998 Confocal microscopy demonstrated that exogenous EB3, like EB1, is associated with the cytoplasmic microtubule network. |
| GO:0005881 cytoplasmic microtubule | IBA GO_REF:0000033 | ACCEPT | Summary: Cytoplasmic microtubule (IBA) from the RP/EB family node. Reason: Mammalian EB3 associates with the cytoplasmic microtubule network, and mapre3b keeps the CH domain that mediates microtubule binding. Supporting Evidence: PMID:10644998 Confocal microscopy demonstrated that exogenous EB3, like EB1, is associated with the cytoplasmic microtubule network. file:DANRE/mapre3a/mapre3a-bioinformatics/RESULTS.md Both copies keep the microtubule-binding CH domain, the EBH dimerization/partner-binding domain and the C-terminal aromatic tail. |
| GO:0008017 microtubule binding | IEA GO_REF:0000002 | ACCEPT | Summary: Microtubule binding from InterPro EB1 C-terminal / MAPRE family signatures. Reason: Correct parent of the more specific microtubule plus-end binding (IBA). The CH domain responsible for microtubule binding is conserved in this copy. Supporting Evidence: PMID:19255245 Furthermore, we demonstrated in vitro and in cells that the EB plus-end tracking behavior depends on the calponin homology domain but does not require dimer formation. file:DANRE/mapre3a/mapre3a-bioinformatics/RESULTS.md Both copies keep the microtubule-binding CH domain, the EBH dimerization/partner-binding domain and the C-terminal aromatic tail. |
| GO:0031110 regulation of microtubule polymerization or depolymerization | IBA GO_REF:0000033 | ACCEPT | Summary: Regulation of microtubule polymerization or depolymerization (IBA), donors include human MAPRE1 and MAPRE3 and yeast Bim1. Reason: The main activity of mammalian EB1 and EB3 in cells is suppression of catastrophes, which promotes persistent microtubule growth; dimerization through the EBH domain is required. mapre3b keeps both the CH and EBH domains. Core process, shared with mapre3a. No zebrafish measurement exists. Supporting Evidence: PMID:19255245 Protein depletion and rescue experiments showed that EB1 and EB3, but not EB2, promote persistent microtubule growth by suppressing catastrophes. file:DANRE/mapre3a/mapre3a-bioinformatics/RESULTS.md Both copies keep the microtubule-binding CH domain, the EBH dimerization/partner-binding domain and the C-terminal aromatic tail. |
| GO:0035371 microtubule plus-end | IBA GO_REF:0000033 | ACCEPT | Summary: Microtubule plus-end (IBA), family node PTN000065701. Reason: Plus-end tracking is the defining behaviour of EB proteins and depends on the CH domain, which mapre3b keeps. Core location. Supporting Evidence: PMID:19255245 Furthermore, we demonstrated in vitro and in cells that the EB plus-end tracking behavior depends on the calponin homology domain but does not require dimer formation. file:DANRE/mapre3a/mapre3a-bioinformatics/RESULTS.md Both copies keep the microtubule-binding CH domain, the EBH dimerization/partner-binding domain and the C-terminal aromatic tail. |
| GO:0035372 protein localization to microtubule | IBA GO_REF:0000033 | ACCEPT | Summary: Protein localization to microtubule (IBA); EBs recruit other +TIPs to plus ends. Reason: EBs are the hub of plus-end tracking networks: the EBH domain and C-terminal EEY/F tail bind partner +TIPs, which the EBs recruit to growing ends. mapre3b keeps the EBH domain and the aromatic C-terminal tail. Accepted as a core process for the family; not tested in zebrafish. Supporting Evidence: PMID:19255245 End binding proteins (EBs) are highly conserved core components of microtubule plus-end tracking protein networks. PMID:19255245 EBs terminate with a flexible acidic tail containing the C-terminal EEY/F sequence, which is important for self-inhibition and binding to various partners file:DANRE/mapre3a/mapre3a-bioinformatics/RESULTS.md Both copies keep the microtubule-binding CH domain, the EBH dimerization/partner-binding domain and the C-terminal aromatic tail. |
| GO:0051010 microtubule plus-end binding | IBA GO_REF:0000033 | ACCEPT | Summary: Microtubule plus-end binding (IBA); many donors across eukaryotes including human MAPRE1/MAPRE3. Reason: Core molecular function of EB proteins, conferred by the CH domain; mapre3b keeps it (CH domain about 90% identical to human MAPRE3). Shared with mapre3a. Supporting Evidence: PMID:19255245 Furthermore, we demonstrated in vitro and in cells that the EB plus-end tracking behavior depends on the calponin homology domain but does not require dimer formation. file:DANRE/mapre3a/mapre3a-bioinformatics/RESULTS.md Both copies keep the microtubule-binding CH domain, the EBH dimerization/partner-binding domain and the C-terminal aromatic tail. |
| GO:0051225 spindle assembly | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Spindle assembly (IBA), donors fly EB1 and Dictyostelium EB1. Reason: The node is placed deep in the RP/EB family and the domains are conserved in mapre3b, so there is no sequence-based reason to reject it. However, the vertebrate evidence for a mitotic spindle role concerns mainly EB1 (MAPRE1), and mammalian EB3 is best known as a neuron-enriched +TIP. Kept as a plausible, non-core family role; no zebrafish data. Same call for mapre3a. Supporting Evidence: PMID:12684451 Using EB3-GFP as a marker of microtubule growth in live cells, we subsequently analyze microtubule dynamics in neurons. file:DANRE/mapre3a/mapre3a-bioinformatics/RESULTS.md Both copies keep the microtubule-binding CH domain, the EBH dimerization/partner-binding domain and the C-terminal aromatic tail. |
| GO:0051233 spindle midzone | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Spindle midzone (IBA), donors yeast Mal3 and Bim1. Reason: Seeded by the fungal EB orthologues. The family function (plus-end binding) is conserved in mapre3b, and EBs decorate growing spindle microtubules, but no vertebrate EB3 data address the midzone specifically. Kept as a non-core location. Same call for mapre3a. Supporting Evidence: PMID:19255245 End binding proteins (EBs) are highly conserved core components of microtubule plus-end tracking protein networks. file:DANRE/mapre3a/mapre3a-bioinformatics/RESULTS.md Both copies keep the microtubule-binding CH domain, the EBH dimerization/partner-binding domain and the C-terminal aromatic tail. |
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Download this section (compressed HTML)Q: Where are mapre3a and mapre3b expressed at cellular resolution in larval retina and brain, and does mapre3a mark a neuronal subset that mapre3b lacks?
Q: Is gar MAPRE3 maternally deposited like mapre3b, which would make the zygotic-only onset of mapre3a a derived state?
Experiment: Express tagged Mapre3a and Mapre3b in zebrafish cells or embryos and compare comet velocity, lifetime and catastrophe frequency; test whether either rescues EB3 depletion in mammalian cells.
Hypothesis: mapre3a and mapre3b encode equivalent plus-end tracking proteins.
Type: biochemical/cell-biological comparison
Experiment: Generate mapre3a and mapre3b single and double mutants (including promoter-less or RNA-less alleles to avoid transcriptional adaptation) and assay axon growth and retinal lamination.
Hypothesis: The copies are partly redundant in neurons.
Type: genetic interaction
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