Ecdysone 20-monooxygenase activity during larval-pupal-adult development of the tobacco hornworm,Manduca sexta

Abstract

Ecdysone 20‐monooxygenase is the insect cytochrome P‐450 dependent steroid hydroxylase system responsible for the conversion of ecdysone to 20‐hydroxyecdysone. Using an in vitro radioassay, the levels of ecdysone 20‐monooxygenase activity were quantified during embryogenesis in the egg, and in the fat body and midgut tissues during the fourth larval, fifth larval, and pupal‐pharate adult stadia of the tobacco hornworm Manduca sexta. Although basal, ecdysone 20‐monooxygenase activity was detected during the latter stages of larval embryogenesis. Postembryologically, a single major peak or increase was detected in both fat body and midgut tissues during each stadium. In the fourth larval instar, both fat body and midgut ecdysone 20‐monooxygenase activities were found to peak in the latter half of the stadium at the time of spiracle apolysis; both activities dropped to basal levels by the time of ecdysis. During the fifth larval stadium, fat body steroid hydroxylase activity was found to rise during the feeding stage (days 1–4), then dropped back to basal levels by the onset of pharate pupal development on day 7 of the stadium. Midgut monoooxygenase activity during the fifth larval stadium, however, remained basal during the feeding stage, then rose dramatically to peak on day 5 with the onset of wandering, then dropped back to basal levels by the onset of pharate pupal development. Both fat body and midgut hydroxylase activities were basal during the pupal stage and only rose late in pharate‐adult development, just prior to adult eclosion. Arch. Insect Biochem. Physiol. 41:24–32, 1999. © 1999 Wiley‐Liss, Inc.

The Halloween genes code for cytochrome P450 enzymes mediating synthesis of the insect moulting hormone

“…There is a remarkable correlation between changes in the activity [29,30] and the levels of shd mRNA in the fat body and midgut during the fifth instar and the first 6 days of pupal-adult development ( Figure 2). This suggests that the activity of the Manduca E20MO is strictly dependent on the transcriptional activity, although posttranscriptional control may also occur.…”

Sequence and Structure of the Tobacco Hornworm, Manduca sexta, Transhydrogenase Gene

“…Furthermore, it has been shown that these increases in activity are the result of de novo enzyme synthesis and coincide with increases in both E20-M activity and its encoding gene, shade. 7,12 Research detailing the role of the cytochrome P-450 steroid hydroxylase E-20M has established its role in the NADPH-dependent conversion of the molting hormone, ecdysone, to its physiologically active form, 20-HE. 3,[16][17][18] Because this activity requires NADPH, and is predominantly associated with the mitochondria of the ecdysone target tissues such as midgut, fatbody, and Malphighian tubules 5,19 an association with the reversible transhydrogenase seems likely.…”

Effects of Quinizarin and Five Synthesized Derivatives on Fifth Larval Instar Midgut Ecdysone 20-Monooxygenase Activity of the Tobacco HornwormManduca sexta

“…The nature, regulation, and molecular biology of E20M were elucidated predominantly employing the tobacco hornworm, Manduca sexta, as the model [3][4][5][6][7][8]. Indeed, the developmental impact of E20M was made evident in midgut tissue of the M. sexta fifth larval instar where E20M activity increases 50-fold between days four and five of the stadium and this increase is inextricably tied to the onset of wandering stage behavior [1,8,9]. Moreover, the timing conferred by pulses of 20E was found to be critical to all stages of insect development [1,10].…”