Article

Identification of ecdysis-triggering hormone from an epitracheal endocrine system

Department of Entomology, University of California, Riverside 92521, USA.
Science (Impact Factor: 31.48). 02/1996; 271(5245):88-91. DOI: 10.1126/science.271.5245.88
Source: PubMed

ABSTRACT Developing insects repeatedly shed their cuticle by means of a stereotyped behavior called ecdysis, thought to be initiated by the brain peptide eclosion hormone. Here an ecdysis-triggering hormone, Mas-ETH, is described from the tobacco hornworm Manduca sexta. Mas-ETH contains 26 amino acids and is produced by a segmentally distributed endocrine system of epitracheal glands (EGs). The EGs undergo a marked reduction in volume, appearance, and immunohistochemical staining during ecdysis, at which time Mas-ETH is found in the hemolymph. Injection of EGs extract or synthetic Mas-ETH into pharate larvae, pupae, or adults initiates preecdysis within 2 to 10 minutes, followed by ecdysis. Sensitivity to injected Mas-ETH appears much earlier before ecdysis and occurs with shorter latency than that reported for eclosion hormone. The isolated central nervous system responds to Mas-ETH, but not to eclosion hormone, with patterned motor bursting corresponding to in vivo preecdysis and ecdysis. Mas-ETH may be an immediate blood-borne trigger for ecdysis through a direct action on the nervous system.

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    • "In this study, analysis of the test insect fed with C. microphylla extracts, revealed a developmental disruption in which the insects died (between 10 and 25 ppm) during pharate conditions after initiation of molting (the apolysis step), without completion of morphogenesis . During a molt, ecdysteroid levels first rise to stimulate onset of apolysis and cuticle synthesis, but then must fall to facilitate the release of eclosion hormone (EH) (Truman et al., 1983; 2002) and the ecdysis-triggering hormone (ETH) (Zitnan et al., 1996, 1999). These last substances act in concert to trigger insect ecdysis during the final stages of the molt. "
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    • "Instead, neurosecretory cells that send axons to a release site are located mainly in the pars intercerebralis, but some are also located in the pars lateralis or tritocerebrum, in the suboesophageal and/or ventral ganglia. Non-neuronal Inka cells that produce the releasing hormone ecdysis-triggering hormone (ETH) are located on the surface of insect tracheae [102]. The gut is also a site of synthesis and release (into the hemolymph) of some brain-gut peptides. "
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    • "in Manduca sexta [30] [31] and Drosophila melanogaster [20] [22]. Blood-borne ETHs initiate the ecdysis sequence through direct actions on the central nervous system (CNS) [30] [31]. Discovery of ETH receptor genes in Drosophila [12] [23] and Manduca [13] facilitated identification of many neuronal targets of ETH within the CNS. "
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