A new chitinase-related gene, BmChiR1, is induced in the Bombyx mori anterior silk gland at molt and metamorphosis by ecdysteroid.

A novel ecdysteroid-inducible gene was isolated from the anterior silk gland of the silkworm by mRNA differential display and named Bombyx mori chitinase-related gene 1 (BmChiR1). cDNA for BmChiR1 is 3.7 kbp encoding 1080 amino acids. Its predicted protein sequence consists of two tandem-repeated sequences, both showing high similarities to arthropod chitinases but lacking the active site glutamate essential for catalytic activity, suggesting that BmChiR1 protein has no chitinolytic activity. BmChiR1 mRNA was expressed simultaneously with chitinase mRNA in the anterior silk gland at the ends of the penultimate and last larval instar. Injection of 20-hydroxyecdysone (20E) into feeding last instar larvae induced accumulation of BmChiR1 mRNA. Topical application of a juvenile hormone analog, fenoxycarb, just after the 20E injection, suppressed this induction. BmChiR1 expression is therefore upregulated by ecdysteroid and downregulated by juvenile hormone.