Expression and Alternative Processing of a Chicken Gene Encoding Both Growth Hormone-Releasing Hormone and Pituitary Adenylate Cyclase-Activating Polypeptide

The chicken growth hormone-releasing hormone (GRF) gene was isolated, sequenced, and characterized. In addition, three different mRNAs were isolated from juvenile and adult brain. The first cDNA encoded for a GRF1-46, the second cDNA encoded for a GRF_1-43 due to a sliding intron boundary, and the third skipped exon four and encoded only GRF_33-46. We also determined that juvenile chicken mRNA encoding GRF is expressed in the brain and gonads, but not in the pituitary, heart, liver, kidney, crop, small intestine, large intestine, eye, and muscle. This gene is also interesting in terms of evolution because another neuropeptide, pituitary adenylate cyclase-activating polypeptide (PACAP), is encoded within the same gene (grf/pacap) in chicken, but on a separate gene (pacap) in mammals. We showed previously that these two neuropeptides were encoded in the same cDNA in fish, but the present evidence in chicken suggests a gene duplication in stem mammals.