SrSeptin2 (Salpingoeca rosetta, F2UEE2 / PTSG_07215) - notes

Automated deep research was not available in this session (no provider API
keys configured), so there is no -deep-research-*.md file. These notes were
compiled manually from the cached full text of Booth et al. 2018 (PMID:30281390)
and the UniProt record. SrSeptin6 (F2UDE9, PTSG_06009) was reviewed in the same
session; see genes/SALRS/SrSeptin6/SrSeptin6-notes.md.

Identity

• UniProt F2UEE2 (TrEMBL, unreviewed), 412 aa, ORF PTSG_07215, EMBL EGD74992.1.
  UniProt name "Septin-type G domain-containing protein".
• Literature name SrSeptin2 PMID:30281390.
• Phylogenetic group: the three S. rosetta septins PTSG_04106, PTSG_06009 and
  PTSG_07215 were placed with animal/fungal septins in Groups 1A, 1B and 4,
  respectively PMID:30281390.
  So PTSG_07215 (SrSeptin2) is the Group 4 (Cdc12-family) septin. The
  name "SrSeptin2" therefore does not imply orthology with mammalian SEPT2.
  The UniProt FunFam hit is "septin-7 isoform X1" (3.40.50.300:FF:000162).
• Domains (UniProt): septin-type G domain 21-294 (PS51719) with G1 (31-38),
  G3 (89-92) and G4 (170-173) motifs and PIRSR GTP-binding sites; C-terminal
  disordered region 369-412. The paper describes a C-terminal coiled-coil
  PMID:30281390.
• Family: PANTHER PTHR18884 (SEPTIN); Pfam PF00735; PIRSF006698.

Localisation (only direct evidence)

• N-terminal mTFP1 fusion expressed from a transfected plasmid. Enriched at the
  basal pole of single cells and rosette cells, and at contacts between
  adjacent rosette cells PMID:30281390.
• Also diffuse in the cytosol PMID:30281390.
• Forms filaments that intercalate between cortical microtubules at the basal
  pole PMID:30281390.
• Basal enrichment requires the coiled-coil domain; the deletion forms
  ectopic rings around (presumed) food vacuoles PMID:30281390.
• Colocalises with SrSeptin6; heteromeric assembly is inferred, not shown
  biochemically PMID:30281390.
• Caveat: tagged, plasmid-driven expression; no antibody to endogenous protein.
  The authors argue tagged septins match native localisation in other systems.

Function

• No loss-of-function, biochemical (GTP binding/hydrolysis, filament
  reconstitution) or interaction data for SrSeptin2.
• A role in rosette development is a hypothesis
  PMID:30281390;
  PMID:30281390.

Knockout literature check (2026-10-01)

Searched the cached texts of PMID:32496191 (CRISPR genome editing, full text),
PMID:41037400 (selection-based knockouts, abstract only) and the bioRxiv
preprint DOI:10.1101/2024.07.13.603360 (full text) for "septin", PTSG_07215
and PTSG_06009. None reports a septin knockout; the preprint mentions septins
only in its bibliography (Booth et al. 2018). The full text of PMID:41037400 is
not cached, so its supplementary target list was not checked.

Review decisions (summary)

• GTP binding (IEA, GO_REF:0000120): ACCEPT - intact septin G-domain motifs.
• cytoplasm (ARBA): ACCEPT - tagged protein is cytosolic plus basally enriched.
• cytoskeleton (ARBA): ACCEPT - filaments observed; NEW IDA septin cytoskeleton.
• septin complex (UniRule): ACCEPT - canonical for the family; colocalisation
  with SrSeptin6 consistent.
• NEW: basal part of cell (IDA), septin cytoskeleton (IDA).
• Track C: all rows are IEA from domain/family rules or ARBA; no animal
  tissue or developmental term has propagated. No propagation problem.