Tissue expression of two α-amylase genes in the Pacific oyster Crassostrea gigas. Effects of two different food rations

A semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) assay was developed to estimate tissue-specific expression of two amylase genes in five different tissues of the Pacific oyster Crassostrea gigas and the experimental effects of food level on the cellular, enzymatic and gene expression changes of the digestive gland. Results indicated that both genes were transcribed at different levels depending on tissue type. A strong preferential expression of both amylase genes was observed in the digestive gland leading to high amylase activities, in accordance with the digestive function of this organ. Traces of gene expression and activity were observed in other analysed tissues. These appeared higher in labial palps than in other non-digestive tissues. After 4 weeks of feeding two groups of oysters on either a high or low food level, cellular growth of the digestive gland (+56%) and increase in the total activity of amylase enzymes and in specific amylase activity (+50%) were observed under high food conditions compared to low food conditions. A significant increase (+18%) in the expression of gene A was observed in the digestive gland of oysters fed the high ration compared to that of oysters fed on the low food level whereas no changes in the expression of gene B were observed. Gene A was expressed at a higher level than gene B in all tissues and at all conditions. A role of the amylase gene A in digestive processes and changes in its expression according to food availability is demonstrated in this study. The functional role of the α-amylase B gene remains to be elucidated. Author keywords: α-Amylase; Digestive enzyme activity; Food regulation; Gene expression; Oyster