Immunomodulation with Endogenous Hormone in a Pleuronectiform Fish, the Barfin Flounder

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Barfin flounder, Verasper moseri, is a member of Pleuronectiformes, inhabiting cold sea basin areas. This fish is promising for aquaculture in northern Japan. The present study was undertaken to clarify the relationship between an environmental factor (background color) and the physiological status, including immunomodulation. Of the barfin flounder.As a first step, we determined the primary structure of proopiomelanocortin (POMC), which is a common precursor of several peptide hormones responsible for immunomoduation and body color change, by cDNA cloning. A combination of reverse transcription-polymerase chain reaction and Southern blot analysis showed that the pituitary gland was the major tissue expressing POMC-A and -B genes. The expression of POMC-C gene was observed in all tissues examined In the pituitary, POMC-producing cells were identified in both pars distalis and pars intermedia by immunocytochemistry and in situ hybridization.Rearing of barfin flounder in a tank with a bl … More ack background resulted in higher expression of POMC-A, -B, and -C genes than those with a white background. The expression of POMC-C gene in the skin was higher in the black-reared fish than white-reared fish. These results indicate that background color modulates POMC expression in the pituitary and skin. Thus, body color change of barfin flounder is under the control of paracrine or autocrine systems in addition to endocrine control.Rearing of barfin flounder with a white background resulted in greater somatic growth than those in the black background tank. The expression of melanin-concentrating hormone (MCH), which has been identified as an appetite increasing hormone, was enhanced in the brain of white-reared fish and in fasted fish. Increased MCH in the brain of white background might have augmented the food intake.The effects of POMC-related peptides, which were synthesized based on the cDNA sequence, on barfin flounder leukocytes were also examined. No reproducibility was, however, obtained. Less