Recent sequencing of the genomes of the locust Locusta migratoria and the termite Zootermopsis nevadensis led to the identification of genes that predominantly code for tryptopyrokinins, peptides with a characteristic WFGPRXamide C-terminus (Veenstra 2014). The transcripts and the mature peptides have also been discovered recently in the locust using transcriptome sequencing and mass spectrometry analysis, respectively (Redeker et al., 2017). Two genes encoding tryptoPK precursors were identified in L. migratoria; one encodes 5, and the second 7 tryptoPKs (Veenstra 2014; Redeker et al., 2017). The C-terminal domain of these peptides is highly similar to that of diapause hormone. Hence, it is not yet clear whether this family of peptides activates diapause hormone receptors, or if they have a distinct receptor and, thus, represent a novel signalling system. It is also worth noting that mature tryptoPKs are also encoded on CAPA and pyrokinin/PBAN precursors and hence, it has been suggested that CAPA and pyrokinin genes are ancestors of the tryptoPK genes (Ragionieri et al., 2017; Redeker et al., 2017).
Transcripts encoding tryptoPKs, as well as their mature peptides have been detected in the suboesphageal ganglion (SEG) of Locusta (Redeker et al., 2017). Immunolocalization and mass spectrometry data suggests that tryptoPKs are expressed in a pair of ventral posterior median neurons (VPMN) in the SEG.
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