Testis ecdysiotropin, an insect gonadotropin that induces synthesis of ecdysteroid

M. J. Loeb 1 , A. DeLoof 2 , D.B. Gelman 1 , R.S. Hakim 3 , H. Jaffe 4 , J. P. Kochansky 1 , S.M. Meola 5 , L. Schoofs 2 , X. Vafopoulou 6 , R.M. Wagner 7 & C.W. Woods 8

1. U.S. Dept of Agriculture, Beltsville, MD, 20705, USA; 2. Zool. Inst. Leuven, Belgium; 3. Howard Univ. Washington D.C., 20059, USA; 4. N.I.H., Bethesda MD. 20892, USA; 5. U.S.Dept of .Agriculture. College Station TX 77840, USA; 6. York Univ. Toronto, Canada M3JIP3; 7. U.S.Dept. of Agriculture, Columbia MO 65203, USA; 8. Univ. Md, College Park MD 20742, USA

Insect testes can be induced to synthesize ecdysteroid by a brain neuropeptide, testis ecdysiotropin (TE). Although the original evidence for this peptide came from studies on Lepidoptera, TE also induces ecdysteroid synthesis by gonads of Orthopteran and Heteropteran sp. The predominant compound of the several active peptides isolated from Lymantria dispar brains was a 21 amino acid peptide (ISDFDEYEPLNDADNNEVLDF-OH), Mr 2472 Da (LTE). This molecular sequence is different from those ecdysiotropins that affect the prothoracic glands; it does not activate prothoracic glands. Furthermore, unlike prothoracicotropins, antibody made against synthetic LTE reacts positively with medial as well as lateral neurosecretory cells in the Lepidopteran brain. It also stains cells in the optic lobes and nerves of presumptive antenna and proboscis of pupal L. dispar, and may have a developmental role in addition to its gonadotropic role. Basal ecdysteroid synthesis by Heliothis virescens pupal testes is controlled by positive feedback at a narrow range of high exogenous titers of ecdysteroid, suggesting that high titers of this hormone circulating in the hemolymph prior to the final larval molt and early pupal period coordinate the actions of the gonads with metamorphic events in the whole animal. In L. dispar, LTE induces ecdysteroid synthesis via Gi protein in the presence of low calcium influx to induce release of the second messenger, diacyl glycerol, which in turn results in activation of phosphokinase C. An opposing system appears to be mediated by a peptide similar to the vertebrate hormone angiotensin II. The inhibitory cascade for LTE involves G s protein and its resultant messenger, cyclic AMP, and activates phosphokinase A. The interplay of opposing controls serves to fine tune a system essential to gonadal development and function at appropriate times in the insect life cycle. Gonadal ecdysteroid stimulates the release of growth factor(s) from sheaths of H. virescens testes. These growth factors are necessary to induce mitosis, growth and maturation of the genital tract in tissue culture conditions. At least one of the growth factors produced by the testis sheaths appears to be very much like the vertebrate factor, alpha-1- glycoprotein.

Index terms: Neurosecretion, Maturation, Heliothis virescens, Lymantria dispar

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