Author
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LOEB, MARCIA |
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DELOOF, ARNNOLD - ZOOL.INST.BELGIUM U LEUVE |
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Submitted to: Insect Neurochemistry and Neurophysiology Proceedings
Publication Type: Abstract Only Publication Acceptance Date: 4/1/1997 Publication Date: N/A Citation: N/A Interpretive Summary: Technical Abstract: The brain neuropeptide, testis ecdysiotropin (TE), initiates secretion of ecdysteroids in early last instar testes, and can boost constitutive secretion of immunodetectable ecdysteroid in mid pupal testes in vitro in either Heliothis virescens or Lymantria dispar testes. The post-receptor-binding signalling cascade for TE primarily involves activation of a Gi protein, diacyl glycerol and phosphokinase C in the presence of low titers of calcium. However, a Gs protein-CAMP-phosphokinase A cascade occurs as well. At less than 10-5M, cAMP stimulates ecdysteroido-genesis, but at higher concentrations, cAMP inhibits synthesis and blocks TE. We sought a candidate peptide with such counter control action to TE among available insect peptides to no avail. Surprisingly, the vertebrate peptide, angiotensin II (AII), and the angiotensin converting enzyme (ACE) fit the pattern. ACE has been immunologically identified in high quantity in insect testes and brain. In the absence of testis ecdysiotropin but with either AII or ACE at physiological titers, both larval and pupal testes synthesized immunodetectable ecdysteroid in vitro; however, at increasingly higher concentrations of AII or ACE, ecdysteroid synthesis decreased to 0. Both AII and ACE inhibited TE. However, the AII analog, saralasin, which blocks vertebrate AII receptors, had the same effect in insect testes as AII and ACE. Therefore, the peptide that exerts counter control over testis ecdysteroid secretion in lepidopterans may be similar, but not identical to vertebrate AII, although its precursor appears susceptible to proteolysis by ACE. |
