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Abstract
To elucidate the involvement of amino acid transporter in osmotic adaptation of oysters, the expression of the amino acid transporter gene in response to environmental osmotic changes was investigated. As expected, the expression of the amino acid transporter gene was increased by hyper-osmotic stress, probably to elevate intracellular osmolality. Unexpectedly, the expression was also increased by hypo-osmotic stress, and the level of expression was higher than that induced by hyper-osmotic stress. To identify the region regulating the expression of the oyster amino acid transporter gene in response to changes in environmental osmolality, the 5'-flanking region of approximately 2.3 kb upstream from the translation start site was cloned. Expression vectors with luciferase as a reporter gene driven by 5'-flanking regions with different lengths were constructed and their promoter activities were compared. As a result, the osmo-responsive regulatory region responding to osmolality by both hyper- and hypo-osmolality was found within 132 bp from the transcription start site. [PUBLICATION ABSTRACT]