Molecular cloning and function of ecdysis-triggering hormones in the silkwormBombyx mori

Abstract

SUMMARYInka cells of the epitracheal endocrine system produce peptide hormones involved in the regulation of insect ecdysis. In the silkworm Bombyx mori, injection of Inka cell extract into pharate larvae, pupae or adults activates the ecdysis behavioural sequence. In the present study, we report the identification of three peptides in these extracts, pre-ecdysis-triggering hormone (PETH), ecdysis-triggering hormone (ETH) and ETH-associated peptide(ETH-AP), which are encoded by the same cDNA precursor. Strong immunoreactivity associated with each peptide in Inka cells prior to ecdysis disappears during each ecdysis, indicating complete release of these peptides. Injection of either PETH or ETH alone is sufficient to elicit the entire ecdysis behavioural sequence through the direct action on abdominal ganglia;cephalic and thoracic ganglia are not required for the transition from pre-ecdysis to ecdysis behaviour. Our in vitro data provide evidence that these peptides control the entire ecdysis behavioural sequence through activation of specific circuits in the nervous system. Ecdysis of intact larvae is associated with the central release of eclosion hormone (EH) and elevation of cyclic 3′,5′-guanosine monophosphate (cGMP) in the ventral nerve cord. However, injection of ETH into isolated abdomens induces cGMP elevation and ecdysis behaviour without a detectable release of EH,suggesting that an additional central factor(s) may be involved in the activation of this process. Our findings provide the first detailed account of the natural and hormonally induced behavioural sequence preceding larval,pupal and adult ecdyses of B. mori and highlight significant differences in the neuro-endocrine activation of pre-ecdysis and ecdysis behaviours compared with the related moth, Manduca sexta.

Functional Characterization of Ecdysis Triggering Hormone Receptors (AgETHR-A and AgETHR-B) in the African Malaria Mosquito, Anopheles gambiae

“…This neuropeptide hormone activates ETHR and induces internal signal transduction pathways. Two isoforms of ETHR were reported in other insect species (Zitnan et al, 2002;Kim et al, 2006;Dai and Adams, 2009;Roller et al, 2010;Shi et al, 2017). However, only one ETHR was reported in mites and locust (Veenstra et al, 2012;Lenaerts et al, 2017;Zhu et al, 2019).…”

Neuromodulation and the toolkit for behavioural evolution: can ecdysis shed light on an old problem?

“…More generally, it may be possible to exploit the traditional power of electrophysiological approachesand their application to the identified cells of the crustacean nervous systemto study ecdysis. Extracellular recordings have been effectively used to study fictive ecdysis sequences in reduced preparations of large insects and should be possible in crustaceans [146][147][148]. In addition, transcriptomic approaches can be extended to less studied crustacean species to establish the temporal expression patterns of ecdysis-related genes.…”

The Intricate Role of Ecdysis Triggering Hormone Signaling in Insect Development and Reproductive Regulation

“…Our understanding of the mechanism of endocrine control of ecdysis (pre-ecdysis, ecdysis and post-ecdysis) comes from studies performed on mostly holometabolous insects, such as, moths Manduca sexta and Bombyx mori [ 8 , 9 , 10 , 11 ], fruit fly Drosophila melanogaster [ 12 , 13 , 14 ], and the beetle, Tribolium castaneum [ 15 ]. Four hormones were identified to control various ecdysis sequences: Pre-ecdysis triggering hormone (PETH), Ecdysis triggering hormone (ETH), Eclosion hormone (EH), Bursicon and Crustacean cardioactive peptide (CCAP) [ 16 ].…”

“…Genes encoding ETH and ecdysis triggering hormone receptors (ETHR, ETHR-A, and ETHR-B) were identified and well-characterized in various holometabolous insects, such as moths M. sexta and B. Mori, fruit fly D. melanogaster, red flour beetle Tribolium castaneum, mosquito Aedes aegypti, oriental fruit fly Bactrocera dorsalis , and in a few hemimetabolous insects, such as pea aphid Acyrthosiphon pisum , and desert locust Schistocerca gregoria [ 4 , 8 , 9 , 15 , 20 , 21 , 24 , 25 , 28 , 29 , 30 , 31 ]. In the desert locust, Schistocerca gregaria , the ETHR receptor (SchgrETHR) exhibits dual coupling properties of both cyclic adenosine mono phosphate (cAMP) and Ca 2+ (two second messengers) by increasing their levels, when activated by both SchgrETH1 and SchgrETH2 [ 25 ].…”