Juvenile hormone metabolism during embryogenesis in the tobacco hornworm, Manduca sexta (L.)

Abstract

Juvenile hormones (IH)-l and -111 were metabolized in egg homogenates by two primary routes, ester hydrolysis and epoxide hydration, during embryogenesis of the tobacco hornworm, Manduca sexta (L.). The duration of embryogenesis was 3.5 days at 27OC. Preovipositional and newly oviposited eggs had the highest rate of JH metabolism, which was reduced by day 1 and remained unchanged thereafter. The decline in JH metabolism was the result of a decrease by one-half in the JH esterase activity. JH epoxide hydrolase activity remained unchanged throughout embryogenesis. Ester hydrolysis averaged 1.9 times faster for JH-l than JH-Ill and epoxide hydration 6.6 times faster for JH-Ill than JH-I. There was a sixfold increase in the a-naphthyl acetate (a-NA) esterase activity during the time in embryogenesis when the JH esterase activity was declining or at low levels. Developmental, inhibitor, substrate specificity, gel filtration, and isoelectric focusing studies indicated that the egg JH esterase has some specificity for JH, compared with a-NA, and in part is similar to the hemolymph JH esterase of the adult female. The possible functional role of JH metabolism during embryogenesis is discussed.

Embryonic expression of juvenile hormone binding protein and its relationship to the toxic effects of juvenile hormone in Manduca sexta

“…It is attractive to speculate that during the early phases of embryogenesis, the maternally derived JHBP acts as an effective buffer, constantly binding and releasing the hormone in accordance with equilibrium conditions. Since the corpora allata are not yet functional, no biosynthesis of JH affects this equilibrium; the amount of hormone bound to JHBP reflects the amount sequestered from the maternal hemolymph and the degree of catabolism (Share et al, 1988;. That embryonic JH esterase displays a developmental profile similar to that of JHBP supports the hypothesis that JH esterase and JHBP together regulate bioavailability of the hormone to the developing embryo (Fig.…”

“…In each case, the total JH titer (Bergot et al, 1981) overlays the relevant protein titer. (a) JHBP titers; (b) JH esterase activity (modified from Share et al, 1988); (c) insecticyanin titers (Trost and Goodman, 1986;Trost, unpublished data); (d) total protein. demonstrated to be under the control of JH during the larval stages (Safranek and Riddiford, 1975;Goodman et al, 1987), is compared to that of JH and JHBP in Fig.…”