hbt

Summary: No molecular activity has been established for Headbutt; the ND statement still holds.

Reason: The only gene-specific study (PMID:32761438; PMC full text read, local cache abstract-only) characterises a touch phenotype and the cellular expression pattern and states that the molecular/cellular function of CG43778 had not been studied. Family membership (Rost / PTHR12242) does not supply an activity: the characterised family member Rolling stone (SF46, a different subfamily) has a genetic role in myoblast fusion but no defined biochemical activity, and the HHpred-level resemblance of PTHR12242 to the AIG1/ADTRP FAHFA hydrolases (PMID:27018888) involves a different PANTHER family and could not be reproduced by pairwise alignment (hbt-bioinformatics/RESULTS.md). Accepting the ND is correct.

Summary: The 2012 ND statement is superseded: a 2020 study shows hbt is required for larval head-touch sensitivity, and FlyBase now annotates the gene (on canonical isoform E) to regulation of sensory perception by IMP.

Reason: Zhang et al. 2020 (PMID:32761438) found CG43778 in a larval head-touch screen, named it headbutt, and showed with a MiMIC insertion, a CRISPR full knockout and their trans-heterozygote that loss of hbt halves the gentle-touch response and reduces Ca2+ responses of terminal-organ chordotonal neurons. Headbutt is expressed in sheath/glial cells wrapping the sensory dendrites, not in the neurons, which fits a regulatory role in mechanosensation rather than participation in force transduction. FlyBase attached the resulting IMP to GO:0051931 on the canonical product A0A6H2EJZ8; the knockout removes all isoforms and Q9VK03 carries the whole shared conserved core, so the gene-level process applies to this product too. GO:0051931 regulation of sensory perception is the term the curator chose and is as specific as the evidence (a behavioural and neuronal-response phenotype with a non-neuronal site of expression) supports. The publisher does not permit XML full-text download, so the local cache is abstract-only (the Letter has no abstract text); the findings were read from the PMC HTML full text and are summarised in the notes file, and only the title can be quoted verbatim here.

Proposed replacements: regulation of sensory perception

Summary: Membrane localisation is well supported by the six-helix Rost-family architecture.

Reason: The ISS is from Rolling stone (FBgn0011705), a PTHR12242 family member in a different subfamily (SF46) whose membrane association was shown biochemically (enrichment in embryonic membrane fractions, PMID:9230076). Membrane location is a family-level property (the shared Rost region with six transmembrane helices is complete in Q9VK03 and 30.7% identical to Rost over 218 residues), so the transfer is sound, and PAINT independently places membrane at a PTHR12242 ancestral node (PTN001387085) for the canonical hbt product. Which membrane is not known: the GFP knock-in shows tube- and sheath-like structures around dendrites and glia but was not resolved to plasma or internal membranes, so the general term is as precise as the evidence allows.