JUVENILE-HORMONE REGULATION OF VITELLOGENIN IN THE GYPSY-MOTH, LYMANTRIA-DISPAR - SUPPRESSION OF VITELLOGENIN MESSENGER-RNA IN THE FAT-BODY

Hormonal regulation of vitellogenin synthesis and accumulation in the gypsy moth, Lymantria dispar, was examined using a potent juvenile hormone analogue fenoxycarb. The vitellogenin in the haemolymph of female larvae could be detected on days 4-5 of the 5th (final) larval stadium and continued to accumulate throughout the remainder of the stadium. Treatment of larvae with fenoxycarb during the intermoult period from 4th to 5th instar caused a delay in the appearance of the vitellogenin in the haemolymph and the rate of vitellogenin accumulation decreased. This effect of fenoxycarb was dose responsive and depended on the developmental stage of the larva. Treatment done after day 2 of the 5th stadium had no effect on the vitellogenin accumulation. Analysis of poly(A) RNA isolated from the fat body of female larvae showed the presence of a 5400 nucleotide (nt) RNA species in untreated larvae not present in fenoxycarb-treated larvae. This RNA species was not detected in the fat body of day 7 5th-instar male and day 1 5th-instar female larvae but was present in females on day 6 and later part of the 5th stadium. Translation of poly(A) RNA from untreated female larvae yielded a protein of 175 kDa whereas poly(A) RNA from fenoxycarb-treated female larvae did not. The presence of the 175 kDa product depended upon the presence of the 5400 nt RNA species in the poly(A) RNA. The 175 kDa translation product was immunologically related to the large subunits of the vitellogenin. A synthetic oligonucleotide probe encoding the amino acid sequence corresponding to the N-terminal region of the large subunit of vitellogenin (Vg190) hybridized specifically to the 5400 nt RNA. These data indicate that fenoxycarb acts by regulating the level of vitellogenin mRNA in the fat body.