Abstract
Allatostatins (ASTs) are pleiotropic insect neuropeptides that are potent myoinhibitors of muscle contractions. In this study, we identified and immunolocalized peptides from the MIP/AST and PISCF/AST families in the nervous system of a model beetle, Tenebrio molitor. Neurons containing MIPs were immunolocalized in the brains of adults and the ventral nerve cords of larvae, pupae and imagines of this species as well as in the retrocerebral complex. PISCFs were immunolocalized in the ventral nerve cord of all stages as well as the brain of the adult beetle. Faint signals were also observed in the corpus allatum but not in the corpus cardiacum. The results allowed us to deduce the sequences of three neuropeptides belonging to MIP/ASTs, Tenmo-MIP4—NWGQFGXWa, Tenmo-MIP5—SKWDNFRGSWa and Tenmo-MIP6—EPAWSNLKGIWa, and one peptide from the PISCF/AST family, QSRYXQCYFNPISCX. Furthermore, we showed for the first time myostimulatory action of endogenous MIP/ASTs. Tenmo-MIP5 caused dose-dependent stimulation of the contractile activity of the beetle oviduct muscles, showing a sigmoidal curve up to 81.20% at the 10−8 M concentration, and the EC50 value for the myostimulatory effect of this peptide was 8.50 × 10−12 M. This is the first report of myostimulatory action of an endogenous myoinhibitory peptide in insect muscles.
Highlights
One of the crucial types of compounds in the nervous system of living organisms are neuropeptides
We focus on identification on mRNA level and localization of allatostatins in the nervous system of the Tenebrio molitor beetle in all postembryonic developmental stages, and we show for the first time that endogenous ASTs may act as myostimulators in the insect body
Using RNA isolated from the brains and retrocerebral complexes corpus cardiacum/corpus allatum (CC/corpora allata (CA)) of adults and ventral nerve cords (VNCs) of postembryonic developmental stages of the T. molitor beetle and primers based on T. castaneum MIP/AST and PISCF/AST prehormones, the cDNAs encoding part of the MIP/AST and PISCF/AST were isolated and sequenced by reverse transcription PCR
Summary
One of the crucial types of compounds in the nervous system of living organisms are neuropeptides They play a fundamental role in the control of physiological processes, and they constitute one of the most diverse groups of signaling molecules in terms of function [1,2,3]. Coast and Schooley [10] tried to standardize the classification of all insect neuropeptides, with ASTs among them They changed the name of A-type allatostatins to FGL/ASTs because of the presence of specific amino acid sequence (FGL) at the C-terminus. For the B-type allatostatins the Authors proposed the MIP/ASTs name due to the myoinhibitory action of peptides from this family on insect muscles [10]. The obtained results regarding myostimulatory activity are supported by the presence of neuropeptides in the nervous system of the beetle
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