A novel putative insect chitinase with multiple catalytic domains: hormonal regulation during metamorphosis
Résumé
We have used differential display to identify genes that are regulated by juvenile hormone in the epidermis of the beetle Tenebrio molitor. One of the genes encodes T. molitor chitinase 5 (TmChit5), a chitinase possessing an unusual structure. Sequence analysis of TmChit5 identified five 'chitinase units' of approx. 480 amino acids with similarity to chitinase family 18. These units are separated by less conserved regions containing putative PEST (rich in proline, glutamic acid, serine and threonine) sequences, putative chitin-binding domains and mucin domains. Northern-blot analysis identified a single transcript of approx. 9 kb, whose abundance correlated with that of 20-hydroxyecdysone during metamorphosis. Injection of pupae with 20-hydroxyecdysone alone, or in combination with cycloheximide, indicated that TmChit5 expression is directly induced by the hormone. Further experiments indicated that methoprene (a juvenile hormone analogue) indirectly induced TmChit5 mRNA expression. On the basis of the present results and previous studies, we propose a molecular mechanism for cuticle digestion during the moulting process.
Mots clés
Amino Acid Sequence
Animals
Blotting
Northern
Catalytic Domain
Chitinase/*chemistry/genetics/*metabolism
Cloning
Molecular
Cycloheximide/pharmacology
DNA
Complementary/metabolism
Epidermis/metabolism
Gene Expression Profiling
Gene Library
Hormones/*metabolism
Insect Proteins/*chemistry/genetics/*metabolism
Insects
Metamorphosis
Biological
Methoprene/pharmacology
Molecular Sequence Data
Phylogeny
Protein Structure
Tertiary
Protein Synthesis Inhibitors/pharmacology
RNA
Messenger/metabolism
Tenebrio/metabolism