JUVENILE-HORMONE ACID - EVIDENCE FOR A HORMONAL FUNCTION IN INDUCTIONOF VITELLOGENIN IN LARVAE OF MANDUCA-SEXTA

In the tobacco hornworm (Manduca sexta), vitellogenin (Vg), the major yolk protein precursor, and its mRNA are first detectable in the prepu pal stage; and production of both can be enhanced by methoprene, a juv enile hormone (JH) analog. Competence to respond to methoprene is acqu ired after ecdysteroid-initiated commitment for metamorphosis. Here we show that acquisition of competence requires prior exposure to JH-II acid in addition to ecdysteroid. Application of 20-hydroxyecdysone or RH5992, an ecdysteroid analog, to isolated abdomens from feeding larva e (precommitment) results in exposure of the dorsal vessel (EDV), a si gn of metamorphic commitment-but such abdomens do not make Vg in respo nse to methoprene. However, injection of JH-II acid along with 20-hydr oxyecdysone into isolated abdomens causes Vg production in response to methoprene. Methoprene acid similarly induces competence to respond t o methoprene. Northern blot analysis confirmed that Vg transcripts are present in fat body only if isolated abdomens were pretreated with bo th ecdysteroid, and JH-II acid or methoprene acid. The latter two can induce competence even in precocious prepupae resulting from removal o f the corpora allata (the glands that produce JH) from early penultima te larvae. JH-III acid and related metabolites such as farnesol, farne soic acid, and methyl farnesoate do not induce competence. Hitherto, J H acids have been regarded as precursors or catabolites of JHs. Here w e show for the first time that JH acid has a hormonal function that ca nnot be performed by JH itself. (C) 1998 Wiley-Liss, Inc.