A cholecystokinin (CCK) precursor cDNA was identified from the brain of Japanese flounder (Paralichthys olivaceus). The full open reading frame was obtained by a combination of 3′ and 5′ RACE amplifications and encodes the 136 amino acid precursor. The Japanese flounder CCK-8 amino acid sequence was shown to be Asp-Tyr-Leu-Gly-Trp-Met-Asp-Phe, in which the methionine in the third position of mammalian and amphibian CCK-8 was replaced with leucine, similar to what has been shown in the goldfish. By RT-PCR, expression of CCK precursor mRNA was detected from the brain, stomach and proximal intestine. Whole mount in situ hybridization detected CCK mRNA in scattered cells in the proximal intestine epithelium as well as cerebrum of brain, suggesting the central nervous system and digestive system express the same CCK precursor mRNA.
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