ALLATOTROPIN

Allatotropin is a pleiotropic peptide found in various invertebrates that shows myoregulatory activity. The name derives from its activity in regulating juvenile hormone biosynthesis by corpora allata in insects.

M. sexta allatotropin (Manse-AT) is a tridecapeptide with its C-terminal amidation. The family of this peptides, either isolated or predicted from cDNA sequences and transcriptomic data, have a similar sequence length (13–16 aa residues) and an amidated C-terminus.

Three alternatively spliced mRNAs for Manse-AT have been characterized.3 Each mRNA encodes a precursor protein, from which one copy of Manse-AT is derived. The two longer mRNAs contain the insertion of one or two alternative exons, each of which codes for one or two additional peptides structurally related to Manse- AT (Manse-ATL (AT-like) -I, -II, -III). A cDNA coding for a precursor protein containing Manse-AT and a peptide similar to Manse-ATL-III have been reported in other Lepidoptera, suggesting that the presence of the ATL peptide in addition to AT is not limited to M. sexta.

Manse-AT stimulates JH biosynthesis by adult female CA from many lepidopteran insects, and larval CA from some lepidopteran species.Manse-AT is also reported to stimulate the CA of nonlepidopteran insects, such as the honey bee and blow fly, although no allatotropic peptide has been isolated from these insects.The expression of ATR in the CA observed in some insects readily explains the action of AT on the CA, but its expression in the CC rather than the CA in B. mori does not. In this species, because the ATR-expressing cells in the CC produce short neuropeptide-F (sNPF) and this peptide inhibits the JH synthetic activity of the CA in vitro, it is proposed that ATR may indirectly mediate AT activity on the CA by suppressing sNPF action on the CA.Besides the action on the CA, AT accelerates the heart rate, inhibits ion transport across the midgut epithelium, and controls the release of digestive enzymes in the midgut as well as muscle contraction, eventually affecting feeding behavior.10AT family peptides from hemimetabolous insects such as locust myotropin also show cardiostimulatory and myoregulatory activities.The effects of AT on noninsect invertebrates have been examined using synthetic mosquito AT. This AT showed myoregulatory activity on the turbellarians and hydra.A widespread role of AT in myoregulation and the presence of AT in organisms that do not have JH suggest that the primary role of AT is myoregulation and that the control of JH synthesis is secondary.