Gene Expression of Neuropeptides in the Blood Cells of the Common Carp, Cyprinus carpio

Abstract

Several neuropeptides are reported to function in the immune system of teleost fish. Prolactin-releasing peptide-2 (PrRP2) is thought to be a local modulator of the innate immune response in leukocytes of Atlantic salmon, Salmo salar. We selected the common carp, Cyprinus carpio, as a model organism and examined PrRP2 gene expression in blood cells using reverse transcription polymerase chain reaction (RT-PCR) and DNA sequencing. We also investigated the presence of the PrRP2 peptide using immunocytochemistry. The expression of several other neuropeptides, corticotropin-releasing hormone (CRH), gonadotropin-releasing hormone (GnRH2 and GnRH3), melanin-concentrating hormone (MCH), neuropeptide Y (NPY), orexin (ORX), and thyrotropin-releasing hormone (TRH) was also investigated in blood cells. To account for the possible effects of background color on neuropeptide gene expression, fish were reared on black or white backgrounds for 21 days. PrRP2 expression was observed in blood cells of all individuals. PrRP2 immunoreactivity was detected in granulocytes, lymphocytes, and some unidentified cells. Gene expression of the other neuropeptides, except for GnRH2, was also detected and was not significantly different between fish reared with either background. Our study is the first to demonstrate that several neuropeptides are expressed in blood cells of the common carp.