Abstract
In this study we report on the structural diversity of adipokinetic hormones (AKHs) in the evolutionarily oldest group of social insects, the termites (Isoptera). Using molecular methods combined with in silico bioinformatic analysis, we studied and compared the sequences coding for these neuropeptides in thirteen species of five families of Isoptera. There are three types of AKH octapeptides in termites: Empusa pennata adipokinetic hormone (Emppe-AKH; pQVNFTPNWamide), Microhodotermes viator corpus cardiacum peptide (Micvi-CC; pQINFTPNWamide) and Periplaneta americana cardioaccelerating hormone (Peram-CAH-I; pQVNFSPNWamide). Of these the Peram-CAH-I was the most frequently bioactive form detected in representatives of four out of the six families studied. The complete AKH preprohormones in the termites studied shared at least an 84% amino acid similarity. In agreement with current phylogenetic scenarios of termites as an internal monophyletic clade nested within cockroaches (Blattaria) in the proximity of the family Blattidae, our phylogenetic analysis of the AKH precursor sequences (in the absence of data for the Cryptocercidae) placed the Blattidae (Periplaneta americana) as a sister group of termites and the AKHs of other cockroach families (Blattellidae and Blaberidae) were more divergent from those of termites. Representatives of the basal termite families Mastotermitidae and Archotermopsidae (but also one rhinotermitid genus Prorhinotermes) occurred separately from the phylogenetically advanced lineage (Rhinotermitidae and Termitidae), and Neotermes (Kalotermitidae) was sister to all other termites included.
Highlights
Adipokinetic hormones (AKHs) are well-known insect neuropeptides that have an important role in the control of metabolism
Termites are a species-rich group of social insects that was traditionally classified at the taxonomic rank of order (Isoptera)
A novel type of neurohormone was detected in M. viator (Micvi-CC; pQINFTPNWamide), whereas in M. darwiniensis and T. trinervoides the sequence of Peram-CAH-I was recorded
Summary
Adipokinetic hormones (AKHs) are well-known insect neuropeptides that have an important role in the control of metabolism. AKHs are synthesized, stored and released predominantly from the paired endocrine retrocerebral glands, corpora cardiaca (CC), and there are small amounts of AKH reported in the brains of some insect species (Moshitzky et al, 1987; Kodrík et al, 2015). AKH is synthesized as a preprohormone consisting of a hydrophobic signal peptide, a bioactive neuropeptide and an AKH-associated peptide (Van der Horst et al, 2001). The signal peptide is removed co-translationally and the remaining prohormone is stored in the CC. The bioactive peptide is cleaved from the prohormone prior to its release into the hemolymph (O’Shea & Rayne, 1992; Oudejans et al, 1999)
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