Presence of GH-dependent IGF-II mRNA in the diffuse pancreatic tissue of a teleost

Previously, insulin-like growth factor II (IGF-II) mRNA steady state levels were found to be elevated in the pyloric caeca and surrounding diffuse pancreatic and adipose tissues of rainbow trout treated with bovine growth hormone (bGH) (Shamblott MJ, Cheng CM, Bolt D, Chen TT. Proc Natl Acad Sci USA 1995;A 92:6943-6946). We now report on the GH-dependent expression of IGFs in the pyloric caeca and the surrounding diffuse pancreatic tissue, using a non-radioactive in situ hybridization method employing IGF-I, IGF-II, and insulin specific digoxigenin-labeled antisense cRNA probes. IGF-II mRNA was localized to diffuse pancreatic tissue and to a lesser extent to epithelial cells of the pyloric caeca in rainbow trout treated with bGH. IGF-II mRNA was also detected in epithelial cells of the pyloric caeca in control trout. IGF-I mRNA was undetectable in the pyloric caeca or pancreatic tissue of bGH treated or control rainbow trout. Insulin specific cRNA probes were used in situ to confirm the specificity of IGF-II mRNA expression. We hypothesize that IGF-II may be acting in a local manner as a GH-dependent growth factor in the pancreatic tissue surrounding the pyloric caeca and within the pyloric caeca. Copyright (C) 1999 Elsevier Science Inc.