id: Q08BH0 gene_symbol: tusc2a product_type: PROTEIN status: DRAFT taxon: id: NCBITaxon:7955 label: Danio rerio description: 'tusc2a is one of two zebrafish co-orthologs of human TUSC2 (FUS1), a small (111-residue) N-myristoylated mitochondrial protein. It keeps the N-terminal myristoylation glycine and the acidic calcium-binding motif (DEDGDLAHEFYEE) that define the TUSC2 family. In mammals TUSC2 localizes to mitochondria and regulates mitochondrial calcium uptake and calcium-coupled mitochondrial parameters (membrane potential, reactive oxygen species, permeability transition), and Tusc2-deficient mice show chronic inflammation, autoimmunity and premature age-related pathologies. Nothing has been measured for the zebrafish protein. tusc2a is the larger maternal TUSC2 transcript in the zebrafish zygote, is low during gastrulation and organogenesis, and is expressed at lower levels than tusc2b in most adult tissues, with its highest levels in testis and ovary.' existing_annotations: - term: id: GO:0003674 label: molecular_function evidence_type: ND original_reference_id: GO_REF:0000015 qualifier: enables review: summary: Root molecular-function term with no-data evidence. action: ACCEPT reason: No molecular activity has been measured for zebrafish Tusc2a, and even for mammalian TUSC2 the calcium-binding activity is inferred from a conserved motif and structural modeling rather than a direct binding assay. The ND row correctly states that the molecular function is unknown. supported_by: - reference_id: PMID:24328503 supporting_text: Based on putative calcium-binding and myristoyl-binding domains that we identified in Fus1, we explored our hypothesis that Fus1 regulates mitochondrial calcium handling and calcium-coupled processes. - term: id: GO:0005739 label: mitochondrion evidence_type: IBA original_reference_id: GO_REF:0000033 qualifier: is_active_in supporting_entities: - MGI:MGI:1931086 - PANTHER:PTN001035705 review: summary: Mitochondrial location propagated from mouse Tusc2. action: ACCEPT reason: Mitochondrial localization is the best-established property of TUSC2 and depends on N-myristoylation. tusc2a keeps the myristoylation glycine and the calcium-binding motif exactly, so it sits inside the clade that inherited the location. Not yet imaged in zebrafish. supported_by: - reference_id: PMID:35181743 supporting_text: Also, myristoylation-deficient FUS1/TUSC2 loses its characteristic mitochondria/ER localization and its abilities to induce apoptosis and suppress tumor cell proliferation in vitro. - reference_id: file:DANRE/tusc2a/tusc2a-bioinformatics/RESULTS.md supporting_text: Both copies keep the myristoylation site and the exact calcium-binding motif. - term: id: GO:0006954 label: inflammatory response evidence_type: IBA original_reference_id: GO_REF:0000033 qualifier: involved_in supporting_entities: - MGI:MGI:1931086 - PANTHER:PTN002693339 review: summary: Inflammatory response propagated from mouse Tusc2, whose knockout shows chronic inflammation and an altered response to asbestos. action: MARK_AS_OVER_ANNOTATED reason: 'The mouse evidence is a knockout phenotype: loss of Fus1 perturbs immune cell numbers and cytokine dynamics, which the authors attribute to disturbed mitochondrial homeostasis. TUSC2 acts on mitochondrial calcium handling within cells; it does not itself carry out steps of the inflammatory response, so this is a downstream consequence rather than participation. For zebrafish there are no immune data at all. The mitochondrial terms describe what the protein does.' propagation_review: root_cause: TERM_SCOPING_PROBLEM failure_modes: - ROLE_CONFLATION source_entities: - source_id: PANTHER:PTN002693339 source_status: SOURCE_WEAK_OR_INFERRED comment: A different node from the one carrying the mitochondrial terms; seeded by the mouse knockout inflammation phenotype, which reflects a downstream consequence of mitochondrial dysfunction. - source_id: MGI:MGI:1931086 source_label: Tusc2 (mouse) source_status: SOURCE_WEAK_OR_INFERRED comment: Knockout mice show chronic inflammation and altered cytokine dynamics; the authors attribute this to disturbed mitochondrial homeostasis rather than a direct role of Tusc2 in the inflammatory response. supported_by: - reference_id: PMID:22513871 supporting_text: Untreated Fus1(-/-) mice had an ~eight-fold higher proportion of peritoneal granulocytes than Fus1(+/+) mice, pointing at ongoing chronic inflammation. - reference_id: PMID:24328503 supporting_text: Our findings suggest that Fus1 achieves its protective role in inflammation, autoimmunity, and cancer via the regulation of mitochondrial calcium and calcium-coupled parameters. - term: id: GO:0051881 label: regulation of mitochondrial membrane potential evidence_type: IBA original_reference_id: GO_REF:0000033 qualifier: involved_in supporting_entities: - MGI:MGI:1931086 - PANTHER:PTN001035705 review: summary: Regulation of mitochondrial membrane potential propagated from mouse Tusc2. action: ACCEPT reason: Loss of Fus1 changes mitochondrial membrane potential together with calcium uptake and ROS in mouse cells. This is the closest existing term to the proposed core role (mitochondrial calcium handling) and the node is appropriate for a protein that keeps both functional motifs. Untested in zebrafish. supported_by: - reference_id: PMID:24328503 supporting_text: The reduced rate of mitochondrial calcium uptake in Fus1-deficient cells correlated with cytosolic calcium increase and dysregulation of calcium-coupled mitochondrial parameters, such as reactive oxygen species production - reference_id: PMID:22513871 supporting_text: Finally, we demonstrated Fus1-dependent basal and asbestos-induced changes in major mitochondrial parameters (ROS production, mitochondrial potential and UCP2 expression) in Fus1(-/-) immune cells and in Fus1-depleted cancer cells core_functions: - description: Myristoylated mitochondrial protein that, by analogy with mammalian TUSC2, regulates mitochondrial calcium uptake and calcium-coupled mitochondrial parameters such as membrane potential; its molecular activity (proposed calcium sensing through the conserved acidic motif) is not established. Both zebrafish copies keep the myristoylation site and the calcium-binding motif. directly_involved_in: - id: GO:0051881 label: regulation of mitochondrial membrane potential locations: - id: GO:0005739 label: mitochondrion supported_by: - reference_id: PMID:24328503 supporting_text: Our results establish Fus1 as one of the few identified regulators of mitochondrial calcium handling. - reference_id: file:DANRE/tusc2a/tusc2a-bioinformatics/RESULTS.md supporting_text: Both copies keep the myristoylation site and the exact calcium-binding motif. references: - id: GO_REF:0000015 title: Use of the ND evidence code for Gene Ontology (GO) terms findings: [] - id: GO_REF:0000033 title: Annotation inferences using phylogenetic trees findings: [] - id: PMID:24328503 title: Fus1/Tusc2 is a novel regulator of mitochondrial calcium handling, Ca2+-coupled mitochondrial processes, and Ca2+-dependent NFAT and NF-κB pathways in CD4+ T cells. findings: [] reference_review: relevance: HIGH correctness: VERIFIED review_notes: Mouse cells; loss of Fus1 reduces mitochondrial calcium uptake. Main evidence for the mitochondrial calcium role. - id: PMID:22513871 title: Tumour suppressor Fus1 provides a molecular link between inflammatory response and mitochondrial homeostasis. findings: [] reference_review: relevance: MEDIUM correctness: VERIFIED review_notes: Abstract only; Fus1 knockout mouse inflammation phenotype and mitochondrial parameters; the likely basis of the mouse inflammatory-response annotation. - id: PMID:35181743 title: 'Mitochondrial Fus1/Tusc2 and cellular Ca2+ homeostasis: tumor suppressor, anti-inflammatory and anti-aging implications.' findings: [] reference_review: relevance: MEDIUM correctness: VERIFIED review_notes: Review by the group that characterized Fus1/Tusc2; myristoylation-dependent mitochondrial localization. - id: PMID:42314984 title: An Evolutionarily Conserved TUSC2-OSCP Interface Suggests a Mitochondrial Ca(2)⁺-Sensing Mechanism for ATP Synthase Regulation. findings: [] reference_review: relevance: MEDIUM correctness: VERIFIED review_notes: Phylogenetic conservation of the acidic calcium-binding motif across metazoans; AI structural modeling of a TUSC2-OSCP interface (a hypothesis, not an experimental result). - id: file:DANRE/tusc2a/tusc2a-bioinformatics/RESULTS.md title: tusc2a / tusc2b protein, expression and synteny comparison reference_review: relevance: HIGH correctness: VERIFIED review_notes: Manual audit verified the sidecar supports both TUSC2 copies retaining the N-myristoylation glycine and exact calcium-binding motif, with double-conserved synteny but only quantitative expression differences. findings: [] suggested_questions: - question: Do zebrafish Tusc2a and Tusc2b both localize to mitochondria, and do both need the N-terminal glycine for it? - question: Is the maternal-biased expression of tusc2a (and the zygotic expression of tusc2b) a partition of an ancestral profile? What does gar TUSC2 expression look like through development and in gonads? - question: Does either copy bind calcium through the conserved DEDGDLAHEFYEE motif? suggested_experiments: - hypothesis: Both copies regulate mitochondrial calcium uptake. description: Make tusc2a, tusc2b and double mutants (including maternal-zygotic tusc2a); measure mitochondrial calcium uptake and membrane potential in embryonic cells with genetically encoded sensors. experiment_type: genetic interaction - hypothesis: The proteins are interchangeable. description: Rescue double-mutant mitochondrial phenotypes with either coding sequence, and with a Gly2Ala myristoylation mutant as a control. experiment_type: cross-rescue