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The Journal of Experimental Biology 205, 3459-3473 (2002)
Copyright © 2002 The Company of Biologists Limited

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

Duan itan^1,*, Laura Hollar², Ivana Spalovská^1,4, Peter Taká¹, Inka itanová^1,5, Sarjeet S. Gill³ and Michael E. Adams^2,3

¹ Institute of Zoology, Slovak Academy of Sciences, Dúbravská cesta 9, 84206 Bratislava, Slovakia
² Department of Entomology, 5429 Boyce Hall, University of California, Riverside, CA 92521, USA
³ Department of Cell Biology and Neuroscience, 5429 Boyce Hall, University of California, Riverside, CA 92521, USA
⁴ Department of Zoology, Comenius University, Mlynská dolina B2, 84215 Bratislava, Slovakia
⁵ Institute of Medical Chemistry and Biochemistry, School of Medicine, Comenius University, Sasinkova 2, 81108 Bratislava, Slovakia

^* Author for correspondence (e-mail: dusan.zitnan{at}savba.sk)

Accepted 8 August 2002

Inka 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.

Key words: Inka cells, pre-ecdysis-triggering hormone, ecdysis-triggering hormone, cGMP, behaviour, Bombyx mori

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