THE EFFECTS OF A DUPLICATION IN THE OVINE GROWTH-HORMONE (GH) GENE ONGH EXPRESSION IN THE PITUITARIES OF RAM LAMBS FROM LEAN AND FAT-SELECTED SHEEP LINES

Growth hormone (GH) gene expression was investigated in pituitaries of 14- to 15-month-old ram lambs from flocks selected for high (fat) or low (lean) back fat depth, which were also homozygous for a single GH gene allele, heterozygous or homozygous for a duplication in the GH ge ne. The pituitaries of lean sheep of all three GH genotypes were signi ficantly heavier than those of fat sheep, but there were no pituitary weight differences between GH genotypes. No significant lean-fat selec tion line- or GH genotype-specific differences were measured in pituit ary GH concentration. However there was a significant increase (P < 0. 01) in the total pituitary content of GH in lean compared with fat ani mals and a significant interaction between GH genotype and lean-fat se lection line (P < 0.05) was noted for GH content. No significant diffe rences were measured in the relative concentration of GH mRNA, suggest ing that the ratio of GH mRNA per mg total cellular RNA remained const ant across lean-fat selection line and GH genotype. We conclude that t he pituitary glands of Coopworth sheep selected for low backfat depth (lean) are bigger and have an increased GH content, but appear to cont ain similar concentrations of GH mRNA and immunoreactive GH as the pit uitaries of fat sheep. The presence of the GH gene duplication in shee p has little measurable effect on the expression and storage of GH in the pituitary. (C) Elsevier Science Inc. 1997.