{"gene":"TG_205670","gene_symbol":"SFA2","run_date":"2026-09-08T11:06:16","timeline":{"discoveries":[{"year":2012,"finding":"TgSFA2 (striated fiber assemblin 2) polymerizes into a dynamic fiber that emerges from centrosomes immediately after their duplication and grows in a polarized fashion, with daughter cells forming at its distal tip; daughter cells remain physically tethered at their apical end (conoid and polar ring) to the fiber.","method":"Live imaging and genetic experiments in Toxoplasma gondii","journal":"PLoS Biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic loss-of-function with defined cellular phenotype plus direct localization experiments, published in peer-reviewed journal with clear mechanistic demonstration","pmids":["23239939"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2012,"finding":"Genetic ablation of TgSFA2 blocks cytokinesis at its earliest point — the initiation of the daughter microtubule organizing center (MTOC) — while mitosis proceeds unimpeded, causing accumulation of multiple nuclei without daughter cell formation.","method":"Genetic knockout/conditional knockdown with phenotypic readout (nuclear accumulation, absence of daughter cell budding) in Toxoplasma gondii","journal":"PLoS Biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean loss-of-function with specific, well-defined cellular phenotype (cytokinesis block at MTOC initiation) distinguishing mitosis from cytokinesis, peer-reviewed","pmids":["23239939"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2012,"finding":"TgSFA2 and TgSFA3 are two essential components of the striated fiber assemblin (SFA) fiber that together organize parasite cell division by physically linking centrosome duplication to daughter cell budding.","method":"Genetic epistasis / double mutant analysis and co-localization in Toxoplasma gondii","journal":"PLoS Biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic loss-of-function of two components with defined phenotype in single lab study","pmids":["23239939"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]}],"current_model":"TgSFA2 is an essential component of a striated fiber assemblin (SFA) polymer that nucleates from centrosomes immediately after duplication, grows in a polarized manner toward the daughter cell apical complex, and is required for initiation of the daughter MTOC, thereby coupling centrosome duplication to daughter cell budding during Toxoplasma gondii cell division."},"narrative":{"mechanistic_narrative":"TgSFA2 is a striated fiber assemblin that organizes cell division in Toxoplasma gondii by physically coupling centrosome duplication to daughter cell budding [PMID:23239939]. It polymerizes into a dynamic, polarized fiber that emerges from centrosomes immediately after their duplication and grows toward its distal tip, where daughter cells form and remain tethered at their apical end (conoid and polar ring) [PMID:23239939]. Genetic ablation of TgSFA2 blocks cytokinesis at its earliest step — initiation of the daughter microtubule organizing center (MTOC) — while mitosis proceeds unchecked, producing cells with accumulated nuclei but no daughter buds, establishing TgSFA2 as an essential initiator of daughter cell assembly [PMID:23239939]. TgSFA2 acts together with TgSFA3 as an essential component of this SFA fiber [PMID:23239939].","teleology":[{"year":2012,"claim":"It was unknown how centrosome duplication is physically linked to daughter cell formation in Toxoplasma; imaging showed TgSFA2 forms a polarized fiber from newly duplicated centrosomes to which nascent daughters remain apically tethered, establishing a structural connector between the two events.","evidence":"Live imaging and localization in Toxoplasma gondii","pmids":["23239939"],"confidence":"High","gaps":["Molecular mechanism of polarized fiber growth and centrosome nucleation not defined","How daughter apical structures physically attach to the fiber tip not resolved"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2012,"claim":"Whether TgSFA2 was required for division and at which step was unknown; loss-of-function arrested cytokinesis at daughter MTOC initiation while permitting mitosis, pinpointing TgSFA2 as an essential trigger of daughter cell budding rather than a mitotic factor.","evidence":"Genetic knockout/conditional knockdown with nuclear-accumulation phenotype in Toxoplasma gondii","pmids":["23239939"],"confidence":"High","gaps":["The signal that couples fiber assembly to MTOC initiation is unknown","Interacting partners at the daughter MTOC not identified"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2012,"claim":"It was unclear whether TgSFA2 acts alone; epistasis and co-localization showed TgSFA2 and TgSFA3 are both essential components of the same SFA fiber, defining the fiber as a multi-assemblin structure organizing division.","evidence":"Genetic epistasis / double mutant analysis and co-localization in Toxoplasma gondii","pmids":["23239939"],"confidence":"Medium","gaps":["Stoichiometry and higher-order architecture of the SFA2/SFA3 fiber not determined","Single-lab study without independent confirmation"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":null,"claim":"The biochemical basis of SFA fiber polymerization, its nucleation at the centrosome, and the mechanism by which it triggers daughter MTOC initiation remain uncharacterized in the available corpus.","evidence":"","pmids":[],"confidence":"Low","gaps":["No structural model of the SFA fiber","No defined regulators of fiber assembly/disassembly timing","Mechanism coupling fiber to MTOC initiation unresolved"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]}],"mechanism_profile":{"molecular_activity":[],"localization":[],"pathway":[],"complexes":["Striated fiber assemblin (SFA) fiber (with TgSFA3)"],"partners":["TGSFA3"],"other_free_text":["Fiber nucleates from centrosomes immediately after duplication and grows in a polarized manner toward the daughter apical complex [#0].","Essential for initiation of the daughter microtubule organizing center; loss blocks cytokinesis while mitosis continues [#1]."]},"strain_conflicts":[]},"prefetch_data":{},"corpus_meta":[{"pmid":"23239939","id":"PMC_23239939","title":"Cell division in Apicomplexan parasites is organized by a homolog of the striated rootlet fiber of algal flagella.","date":"2012","source":"PLoS biology","url":"https://pubmed.ncbi.nlm.nih.gov/23239939","citation_count":95,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":3005,"output_tokens":781,"usd":0.010365,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":5631,"output_tokens":1782,"usd":0.036353,"stage2_stop_reason":"end_turn"},"total_usd":0.046718,"stage1_batch_id":"msgbatch_01WokvBYTB6JLnYrpD4rXnyV","stage2_batch_id":"msgbatch_01M7hsQDvz6AqVC9DLVjQzzc","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2012,\n      \"finding\": \"TgSFA2 (striated fiber assemblin 2) polymerizes into a dynamic fiber that emerges from centrosomes immediately after their duplication and grows in a polarized fashion, with daughter cells forming at its distal tip; daughter cells remain physically tethered at their apical end (conoid and polar ring) to the fiber.\",\n      \"method\": \"Live imaging and genetic experiments in Toxoplasma gondii\",\n      \"journal\": \"PLoS Biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic loss-of-function with defined cellular phenotype plus direct localization experiments, published in peer-reviewed journal with clear mechanistic demonstration\",\n      \"pmids\": [\"23239939\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Genetic ablation of TgSFA2 blocks cytokinesis at its earliest point — the initiation of the daughter microtubule organizing center (MTOC) — while mitosis proceeds unimpeded, causing accumulation of multiple nuclei without daughter cell formation.\",\n      \"method\": \"Genetic knockout/conditional knockdown with phenotypic readout (nuclear accumulation, absence of daughter cell budding) in Toxoplasma gondii\",\n      \"journal\": \"PLoS Biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean loss-of-function with specific, well-defined cellular phenotype (cytokinesis block at MTOC initiation) distinguishing mitosis from cytokinesis, peer-reviewed\",\n      \"pmids\": [\"23239939\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"TgSFA2 and TgSFA3 are two essential components of the striated fiber assemblin (SFA) fiber that together organize parasite cell division by physically linking centrosome duplication to daughter cell budding.\",\n      \"method\": \"Genetic epistasis / double mutant analysis and co-localization in Toxoplasma gondii\",\n      \"journal\": \"PLoS Biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic loss-of-function of two components with defined phenotype in single lab study\",\n      \"pmids\": [\"23239939\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    }\n  ],\n  \"current_model\": \"TgSFA2 is an essential component of a striated fiber assemblin (SFA) polymer that nucleates from centrosomes immediately after duplication, grows in a polarized manner toward the daughter cell apical complex, and is required for initiation of the daughter MTOC, thereby coupling centrosome duplication to daughter cell budding during Toxoplasma gondii cell division.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"TgSFA2 is a striated fiber assemblin that organizes cell division in Toxoplasma gondii by physically coupling centrosome duplication to daughter cell budding [#2]. It polymerizes into a dynamic, polarized fiber that emerges from centrosomes immediately after their duplication and grows toward its distal tip, where daughter cells form and remain tethered at their apical end (conoid and polar ring) [#0]. Genetic ablation of TgSFA2 blocks cytokinesis at its earliest step — initiation of the daughter microtubule organizing center (MTOC) — while mitosis proceeds unchecked, producing cells with accumulated nuclei but no daughter buds, establishing TgSFA2 as an essential initiator of daughter cell assembly [#1]. TgSFA2 acts together with TgSFA3 as an essential component of this SFA fiber [#2].\",\n  \"teleology\": [\n    {\n      \"year\": 2012,\n      \"claim\": \"It was unknown how centrosome duplication is physically linked to daughter cell formation in Toxoplasma; imaging showed TgSFA2 forms a polarized fiber from newly duplicated centrosomes to which nascent daughters remain apically tethered, establishing a structural connector between the two events.\",\n      \"evidence\": \"Live imaging and localization in Toxoplasma gondii\",\n      \"pmids\": [\"23239939\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism of polarized fiber growth and centrosome nucleation not defined\", \"How daughter apical structures physically attach to the fiber tip not resolved\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Whether TgSFA2 was required for division and at which step was unknown; loss-of-function arrested cytokinesis at daughter MTOC initiation while permitting mitosis, pinpointing TgSFA2 as an essential trigger of daughter cell budding rather than a mitotic factor.\",\n      \"evidence\": \"Genetic knockout/conditional knockdown with nuclear-accumulation phenotype in Toxoplasma gondii\",\n      \"pmids\": [\"23239939\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The signal that couples fiber assembly to MTOC initiation is unknown\", \"Interacting partners at the daughter MTOC not identified\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"It was unclear whether TgSFA2 acts alone; epistasis and co-localization showed TgSFA2 and TgSFA3 are both essential components of the same SFA fiber, defining the fiber as a multi-assemblin structure organizing division.\",\n      \"evidence\": \"Genetic epistasis / double mutant analysis and co-localization in Toxoplasma gondii\",\n      \"pmids\": [\"23239939\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Stoichiometry and higher-order architecture of the SFA2/SFA3 fiber not determined\", \"Single-lab study without independent confirmation\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The biochemical basis of SFA fiber polymerization, its nucleation at the centrosome, and the mechanism by which it triggers daughter MTOC initiation remain uncharacterized in the available corpus.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No structural model of the SFA fiber\", \"No defined regulators of fiber assembly/disassembly timing\", \"Mechanism coupling fiber to MTOC initiation unresolved\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005200\", \"supporting_discovery_ids\": [0, 2], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005813\", \"supporting_discovery_ids\": [0], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0000910\", \"supporting_discovery_ids\": [1, 2], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]}\n    ],\n    \"complexes\": [\"Striated fiber assemblin (SFA) fiber (with TgSFA3)\"],\n    \"partners\": [\"TgSFA3\"],\n    \"other_free_text\": [\n      \"Fiber nucleates from centrosomes immediately after duplication and grows in a polarized manner toward the daughter apical complex [#0].\",\n      \"Essential for initiation of the daughter microtubule organizing center; loss blocks cytokinesis while mitosis continues [#1].\"\n    ]\n  },\n  \"strain_conflicts\": []\n}","audit_flag":null,"strains":[{"strain":"ME49","gene_id":"TGME49_205670","name":"SFA2","product":"striated fiber assemblin SFA2","uniprot_acc":"A0A125YS14","chromosome":"TGME49_chrVIIa","start_pos":1222262},{"strain":"GT1","gene_id":"TGGT1_205670","name":null,"product":"SF-assemblin/beta giardin protein","uniprot_acc":null,"chromosome":"TGGT1_chrVIIa","start_pos":1136035},{"strain":"RH88","gene_id":"TGRH88_033830","name":null,"product":"SF-assemblin/beta giardin protein","uniprot_acc":null,"chromosome":"CM023088","start_pos":1304874},{"strain":"VEG","gene_id":"TGVEG_205670","name":null,"product":"SF-assemblin/beta giardin protein","uniprot_acc":"B9Q022","chromosome":"TGVEG_chrVIIa","start_pos":1293768}]}