The baculovirus egt gene encodes an ecdysteroid UDP-glucosyl transferase (EGT) which catalyzes the transfer of sugar from UDP-sugar to ecdysteroid, the insect molting hormone. EGT activity in cells infected with Lymantria dispar nuclear polyhedrosis virus (LdNPV) was demonstrated. Insects infected with LdNPV having EGT activity were inhibited in larval molting and pupation, while infection of insect with a mutant virus lacking EGT activity did not inhibit molting and pupation. Therefore, expression of the egt gene allowed the virus to interfere with normal development of gypsy moth larvae. Insect growth was retarded and slow weight gain was observed in molt-inhibited fourth-instar larvae. LdNPV infection also affected insect hormonal system. The level of hemolymph ecdysteroids in virus-infected larvae was found to be higher than in uninfected controls. Ecdysteroids in these virus-infected insects were composed mostly of ecdysone glucoside, the product of EGT. Little or no free ecdysteroids were detected in hemolymph in late stages of virus infection. Continuous synthesis of ecdysone by the prothoracic gland was observed during virus replication. Gland activity in virus-infected fourth-instar larvae was higher than controls and continued until the late stages of virus infection even after the time controls had ecdysed into fifth instars. During virus replication, the prothoracic gland was observed to maintain morphological and ultrastructural characteristics indicative of ecdysone biosynthetic activities. It was also demonstrated that the ecdysone conjugate present in the hemolymph of virus-infected insects did not serve as a feedback regulator for ecdysone biosynthesis. Although the exact mechanism for the continued activity of the gland is not known, this study suggests that the lack of feedback inhibition by the ecdysone conjugate may play an important role in raising the level of hormone in virus-infected insects. This altered hormonal level, composition, synthesis, and regulation was not observed in insects infected with an egt gene inactivated mutant virus. Therefore, it is apparent that LdNPV modulates the insect hormonal system through the expression of EGT.
| Identifer | oai:union.ndltd.org:UMASS/oai:scholarworks.umass.edu:dissertations-8904 |
| Date | 01 January 1994 |
| Creators | Park, Eun Ju |
| Publisher | ScholarWorks@UMass Amherst |
| Source Sets | University of Massachusetts, Amherst |
| Language | English |
| Detected Language | English |
| Type | text |
| Source | Doctoral Dissertations Available from Proquest |
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