Expression of salmon corticotropin-releasing hormone precursor gene in thepreoptic nucleus in stressed rainbow trout

The behavior of genes encoding the corticotropin-releasing hormone (CRH) pr ecursor in response to stress has not been extensively studied in teleosts. To clarify this problem, CRH cDNAs were isolated from a hypothalamic cDNA library of sockeye salmon, Oncorhynchus nerka, by screening with PCR produc ts amplified from the hypothalamic mRNA with primers deduced from the seque nce of the sucker CRH precursor. Two types of PCR products with a high degr ee of sequence homology were identified (CRH-I and CRH-II). A cDNA encompas sing the entire ceding sequence of the salmon CRH-I precursor was isolated. The salmon CRH-I cDNA encodes a 167-amino-acid precursor, which consists o f a signal sequence, a cryptic peptide, and the carboxyl terminal 41-amino- acid sequence of CRH. The deduced amino acid sequence of salmon CRH peptide exhibits 66 to 80% homology with mammalian, Xenopus, and sucker CRHs, wher eas it shows about 50% homology with sucker, carp, or role urotensin I, a C RH-related neuropeptide in teleost fish. In situ hybridization histochemist ry demonstrated CRH mRNA-positive perikarya in the preoptic nucleus in rain bow trout, Oncorhynchus mykiss, when the fish were stressed by confinement. Adjacent sections hybridized with probes for salmon vasotocin (VT) precurs or showed many VT mRNA-positive neurons also in the preoptic nucleus, sugge sting a colocalization of CRH and VT mRNAs in the same magnocellular neuron s in the rainbow trout brain. The present results suggest that CRH may have important roles in the control of stress responses in salmonid fish. (C) 1 999 Academic Press.