Regulation of the ecdysteroid titer of Manduca sexta: reappraisal of the role of the prothoracic glands.
It is generally accepted that the prothoracic glands of insects produce ecdysone, which is converted by a 20-monooxygenase in peripheral tissues to the major molting hormone, 20-hydroxyecdysone. Incubation in vitro of the prothoracic glands of larval or pupal Manduca sexta in the presence of a hemolymph protein fraction (HPF) increased the ecdysteroid content of the medium almost 8-fold. A comparable increase was noted when HPF was added to medium preconditioned with prothoracic glands but from which the glands had been removed. We used a differential RIA to show that a major product of the prothoracic glands in vitro cross-reacts with antiserum (20-hydroxyecdysone-2-succinylthyroglobulin amide; H-2) that retains affinity to ecdysteroids having a modified A ring. However, this product did not bind to antiserum (ecdysone-22-succinylthyroglobulin amide; H-22) that has affinity mainly for ecdysteroids modified at the side chain. We employed radiolabeled precursor studies with prothoracic glands in vitro and a combination of analytical techniques (NMR, CD, MS) to demonstrate that the major ecdysteroid release from the glands is a mixture of 2-dehydroecdysone and 3-dehydroecdysone (1:2), which is rapidly reduced to ecdysone in the presence of HPF. We postulate that the active component of HPF is 3 beta 3 beta (2 beta)-formin-3(2)-ketoecdysteroid reductase. These results may explain several anomalous observations pertaining to the molting of insect fragments in the absence of prothoracic glands and suggest a complex system for the control of insect molting and metamorphosis.
Department of Biology, University of North Carolina, Chapel Hill 27599-3280.
J T
JT
Warren
S
S
Sakurai
D B
DB
Rountree
L I
LI
Gilbert
S S
SS
Lee
K
K
Nakanishi
D000818:Animals; D004440:Ecdysone / Q000031:analogs & derivatives* / Q000096:biosynthesis / Q000378:metabolism; D004702:Endocrine Glands / Q000502:physiology*; D006458:Hemolymph / Q000032:analysis; D007313:Insecta / Q000254:growth & development / Q000502:physiology*; D007814:Larva; D008675:Metamorphosis, Biological; D010088:Oxidoreductases / Q000378:metabolism; D011679:Pupa
C054761:2-dehydroecdysone; D004440:Ecdysone; C047104:3-dehydroecdysone; D010088:Oxidoreductases