Adipokinetic hormones of the two extant apterygotan insect orders, Archaeognatha and Zygentoma

•AKHs were sequenced via LC-MS from extant apterygotan insects (Archaeognatha and Zygentoma).•The firebrat T. domestica and the bristletail P. maritimus each have one AKH, Peram-CAH-I and Anaim-AKH, respectively.•Immunocytochemistry with an AKH antibody shows the intrinsic CC cells of bristletail, firebrat and silverfish.

Two extant apterygotan insect orders, Archaeognatha and Zygentoma, are investigated with respect to the identity of neuropeptides belonging to the adipokinetic hormone (AKH) peptide family; this is the first report on AKH peptide structures in the so-called primitive insects and the first of any peptide in the Archaeognatha. In the lepismatid, Thermobia domestica, and the machilid, Petrobius maritimus, a single AKH peptide is identified and sequenced from each species; neither sequence is novel and has previously been shown in corpora cardiaca (CC) of cockroaches (Peram-CAH-I) and dragonflies (Anaim-AKH), respectively. These octapeptides differ from each other only in one position (Asn7 in the lepismatid and Ser7 in the machilid). The biological relevance of these peptides was investigated and we speculate that they are likely involved in the mobilisation of lipids in the apterygotes. Immunocytochemistry with an antibody directed against an AKH revealed a well-developed pair of CC in T. domestica and another lepismatid, the fishmoth Ctenolepisma longicaudata; a cluster of immunopositive cells are located retrocerebrally in tissue sections of P. maritimus which may be the CC.

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