The effect of 20-hydroxyecdysone on expression of genes coding for low molecular weight silk proteins of Galleria mellonella

The low molecular weight Galleria silk proteins of 24 and 29–30 kDa are coded by the 1100 nucleotides long mRNAs of the posterior silk gland (PSG) cells. The synthesis of these proteins starts during the first 2 days of the last instar when the endogenous ecdysteroid titre is very low. The synthesis of 24 kDa protein precedes the synthesis of 30 kDa protein. PSGs from day 1 last instar larvae are sensitive to exogenous 20-hydroxyecdysone (20-HE) in vitro at 0.5 μg/ml concentration causing an increase of 1100 nucleotides long mRNAs. The electrophoretic analysis of the in vitro labelling proteins indicates that 20-HE may induced the synthesis of 30 kDa protein. Juvenile hormone II in vitro suppresses the stimulatory effect of 20-HE. PSGs from day 3 last instar larvae are insensitive to exogenous 20-HE in vitro .