The first member of the trissin family was isolated from a purified extract of Drosophila melanogaster (Ida et al., 2011). The ligand was isolated from a fraction that was able to activate the orphan receptor CG34381 (GPCR) in a heterologous calcium assay. A partial amino acid sequence was also obtained following protein sequencing of this active fraction. The cDNA encoding trissin (CG14871) was then cloned using this partial amino acid sequence. The gene encoding trissin has been identified in several arthropods (Roller et al., 2016). Trissin contains six highly conserved cysteine residues that form three disulfide bridges. The trissin signaling system (neuropeptide and its receptor) has been lost in some arthropods, including Rhodnius prolixus and Strigamia maritima.
FlyAtlas expression data indicates that the peptide is highly expressed in the central nervous system (CNS) whereas its receptor is expressed in the CNS and crop of D. melanogaster. Recently, the expression of trissin was mapped in the CNS and gut of Bombyx mori (Roller et al., 2016). Trissin is produced in only two pairs of protocerebral interneurons and four to five neurons in the frontal ganglion (FG) of B. mori. These neurons co-express other neuropeptides.
The physiological role of trissin remains to be determined, but the expression of the peptide in the FG indicates a role in regulation of foregut-midgut contractions and food intake.
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