Differential Expression of the Two Duplicated Insecticyanin Genes,ins-aandins-b,in theBlackMutant ofManduca sexta

Theblack(bl) mutant larvae ofManduca sextaproduces no detectable juvenile hormone (JH) during the molt to the 5th instar. To investigate the JH control of expression of the two insecticyanin genes,ins-aandins-b,developmental changes of the two mRNAs were examined in this mutant. In the epidermis of the freshly ecdysed larvae, the two mRNAs were hardly detectable. Twelve hours after ecdysis, the two mRNAs appeared in low levels and were then gradually increased withins-amRNA rising to a plateau from Day 1 to Day 2 morning andins-bmRNA in Day 2. During these early developmental stages, the epidermal level of the two mRNAs in theblmutant was substantially lower than that observed in the wild-type larvae. On Day 3 of the 5th instar when the larval epidermis becomes pupally committed, the two mRNAs in bothblmutant and wild-type larvae show a similar differential expression pattern. In the fat body, the level of bothins-aandins-bmRNAs was higher than that found in the wild-type larvae. Exogenous JH almost restores the level of the two mRNAs in both epidermis and fat body of the Day 0 5th-instarblmutant larvae to that observed in wild-type animals of the same stage. These results suggest that JH may enhance expression of the two insecticyanin genes in the epidermis but partially repress their expression in the fat body during early development of the wild-type 5th-instar larvae.