Amylase mRNA expression in Crassostrea gigas during feeding cycles

A Crassostrea gigas digestive gland copy DNA (cDNA) library constructed in the lambda phage ZapII (Stratagene, La Jola, USA) was screened with an amylase heterologous proble. To get access to the complete cDNA, a polymerase chain reaction extension was conducted using DNA extracted from the phages. The complete cDNA sequence is 1688 base pairs (EMBL = Y08370). The deduced protein sequence is 519 aminoacids long with a 19 aminoacid signal peptide. Similarity with Pecten maximus amylase is 72%. A 3-day nutrition experiment with a cyclic algal food supply was carried out. Amylase enzyme activities and mRNAs were individually measured on five animals, nine times a day. Messenger RNAs were quantified by dot hybridization using the previously characterized cDNA as probe. Variation of amylase mRNA was observed, in relation with the level of activity of the enzyme. Coordinated changes in RNA and enzyme levels suggested a possible transcriptional regulation of amylase in C. gigas as in vertebrates.