Pro-opiomelanocortin (POMC) is the precursor of a number of biologically active peptides, including adrenocorticotropic hormone, alpha-melanocyte-stimulating hormone and beta-endorphin, which are released by the pituitary glands of fish as well as mammals. To quantify the levels of expression of the two POMC mRNAs relative to one another during the response of the common carp to temperature-induced stress, we used reverse transcriptase PCR combined with capillary electrophoresis and laser-induced fluorescence detection. The ratio of POMC-I mRNA to POMC-II mRNA determined in wild-type and four isogenic carp strains was found to be strain-dependent and influenced by temperature. In strain E20xR8, the ratio had altered in favour of POMC-I from 1:3.2 (POMC-I:POMC-II) in fish adapted to 24 degreesC to 1:1.2 in fish adapted to a decrease of 9 degreesC in ambient temperature. A rapid drop in temperature from 24 to 15 degreesC decreased the POMC mRNA ratio at the expense of POMC-I from 1:1.9 in the control fish (strain E4xR3R8) to 1:4.2 3 h after the temperature drop of 9 degreesC. We conclude that both POMC genes are expressed in the common carp and that their expression ratio is strain-dependent and changes in response to ambient temperature.

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