Control of juvenile hormone production: the relationship between precursor supply and hormone synthesis in the tobacco hornworm, Manduca sexta

Abstract

Tissue culture conditions for the production of juvenile hormone by excised corpora allata from the tobacco hornworm, Manduca sexta, were optimized and hormone output was monitored by incorporation of [ 14C-methyl]-methionine. Production was moderate in early fifth instar but undetectable in late fifth instar larvae. It was low in pupae, unmeasurable in adult males and high in adult females. Hormone production by glands of adult females was unaffected by the presence in the medium of juvenile hormone III, the hormone analogue, Methoprene, dibutyrylcyclic AMP, dibutyryl cyclic GMP and 25-hydroxycholesterol, an inhibitor of cholesterol synthesis in mammals. The assay of the enzyme 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase in homogenates of corpora allata from M. sexta was optimized and activity in homogenates from animals at various life stages was determined. The correlation between the activity of the enzyme and hormone production by intact glands was excellent in all cases examined except for adult males, which have very high HMG-CoA reductase levels, but produce no hormone. Unlike the HMG-CoA reductase of mammalian tissue, the activity of corpus allatum enzyme is unaffected by Mg 2+ ATP or fluoride ion, an inhibitor of phosphoprotein phosphatase. The activity is also unaffected by the presence of cAMP, cGMP, IBMX or 25-hydroxycholesterol.