Corazonin in insects

Corazonin is a peptidergic neurohormone of insects that is expressed in neurosecretory neurons of the pars lateralis of the protocerebrum and transported via nervi corporis cardiaci to the storage lobes of the corpora cardiaca. This peptide occurs with a single isoform in all insects studied so far, with the exception of the Coleoptera in which no corazonin form could be detected. Very few modifications of [Arg⁷]-corazonin, originally isolated from cockroaches, are known, namely [His⁷]-corazonin which is expressed in certain locusts and the stick insect Carausius morosus, and [Thr⁴, His⁷]-corazonin recently described from the honey bee Apis mellifera. In this study, we performed a comprehensive screening for corazonin in the different insect groups after detecting of a fourth isoform in a crane fly, Tipula sp. ([Gln¹⁰]-corazonin). [Arg⁷]-corazonin is distributed in most major lineages of insects, and is thus the ancient form which was present at the time the phylum Insecta evolved. The replacement of Arg with His at position 7 from the N-terminus occurred several times in the evolution of insects. The third isoform, [Thr⁴, His⁷]-corazonin, seems to be restricted to bees (Apidae); whereas wasps (Vespidae) and a bumble bee (Apidae) express other corazonins, specifically [His⁷]-corazonin and [Tyr³, Gln⁷, Gln¹⁰]-corazonin, respectively. A novel corazonin form, [His⁴, Gln⁷]-corazonin, was also detected in all South African members of the newly described insect order Mantophasmatodea. The [His⁴, Gln⁷]-corazonin separates these species from the Namibian Mantophasmatodea which express [Arg⁷]-corazonin and can be used as a distinct character to distinguish these morphologically similar insects.