Developmental expression, alternative splicing and gene copy number for the pituitary adenylate cyclase-activating polypeptide (PACAP) and growth hormone-releasing hormone (GRF) gene in rainbow trout

Both growth hormone-releasing hormone (GRF) and pituitary adenylate cyclase -activating polypeptide (PACAP) are encoded on the same gene in fish, but n ot in mammals. Our objective was to examine the onset and pattern of expres sion for the grf/pacap gene and to determine whether there is more than one gene in rainbow trout. The results show that grf/pacap mRNA is first expre ssed at 4 days after fertilization and continues through to hatching. Alter native splicing at all developmental stages produces a full-length transcri pt and one lacking exon four, which encodes GRF. Thus, independent regulati on of the hormones occurs throughout development. Southern analysis shows t hat two grf/pacap genes exist in trout, but only one gene is responsible fo r the two identified transcripts. Overexpression of the grf/pacap gene in t ransgenic fish was attempted, but did not succeed. We conclude that the ear ly and continued expression of grf/pacap mRNA in trout embryos and regulati on of the neuropeptide ratio suggests they have a role in early brain devel opment apart from their later role in releasing pituitary hormones. (C) 200 1 Elsevier Science Ireland Ltd. All rights reserved.