Direct microinjection has been used to introduce foreign DNA into a number of terminally differentiated cell types as well as embryos of several species including sea urchin, Candida elegans, Xenopus, Drosophila and mice. Various genes have been successfully introduced into mice including constructs consisting of the mouse metallothionein-I (MT) promoter/regulator region fused to either the rat or human growth hormone (hGH) structural genes. Transgenic mice harbouring such genes commonly exhibit high, metal-inducible levels of the fusion messenger RNA in several organs, substantial quantities of the foreign growth hormone in serum and enhanced growth. In addition, the gene is stably incorporated into the germ line, making the phenotype heritable. Because of the scientific importance and potential economic value of transgenic livestock containing foreign genes, we initiated studies on large animals by microinjecting the fusion gene, MT-hGH, into the pronuclei or nuclei of eggs from superovulated rabbits, sheep and pigs. We report here integration of the gene in all three species and expression of the gene in transgenic rabbits and pigs.

Genetic engineering of livestock is expected to have a major effect on the agricultural industry. However, accurate assessment of the consequences of transgene expression is impossible without multigenerational studies. A systematic study of the beneficial and adverse consequences of long-term elevations in the plasma levels of bovine growth hormone (bGH) was conducted on two lines of transgenic pigs. Two successive generations of pigs expressing the bGH gene showed significant improvements in both daily weight gain and feed efficiency and exhibited changes in carcass composition that included a marked reduction in subcutaneous fat. However, long-term elevation of bGH was generally detrimental to health: the pigs had a high incidence of gastric ulcers, arthritis, cardiomegaly, dermatitis, and renal disease. The ability to produce pigs exhibiting only the beneficial, growth-promoting effects of growth hormone by a transgenic approach may require better control of transgene expression, a different genetic background, or a modified husbandry regimen.

Augmentation of vertebrate growth by growth hormone (GH) is primarily due to its regulation of insulin-like growth factor I (IGF I) and IGF II levels. To characterize the effect of GH on the levels of IGF I and IGF II mRNA in a teleost, 10 ,ug of bovine GH (bGH) per g of body weight was administered to juvenile rainbow trout (Oncorhynchus mykiss) through i.p. injection. The levels of IGF I and IGF II mRNA were determined simultaneously, by using RNase protection assays, in the liver, pyloric ceca, kidney, and gill at 0,1,3,6,12,24, 48, and 72 hr after injection. In the liver, IGF I mRNA levels were significantly elevated at 6 and 12 hr (-2-to 3-fold, P 5 0.01), while IGF II mRNA levels were significantly elevated at 3 and 6 hr (-3-fold, P < 0.01). In the pyloric ceca, IGF II mRNA levels were significantly elevated at 12, 24, and 48 hr (-3-fold, P < 0.01), while IGF I mRNA was below the limits of assay accuracy. GH-dependent IGF mRNA appearance was not detected in the gill and kidney. Serum bGH levels, determined by using a radioimmunoassay, were significantly elevated at 3 and 6 hr (P < 0.005). In primary hepatocyte culture, IGF I and IGF II mRNA levels increased in a bGH dose-dependent fashion, with ED50 values of -45 and -6 ng of bGH per ml, respectively. The GH-dependent appearance ofIGF II mRNA in the liver and pyloric ceca suggests important roles for this peptide hormone exclusive of IGF I.Vertebrate growth is primarily controlled by the availability of growth hormone (GH) and the insulin-like growth factors (IGF I and IGF II) to their respective receptors. The secretion of GH from the pituitary, and its subsequent binding to GH receptors, signals the production of IGF I mRNA and polypeptide by liver (endocrine production) and other tissues (autocrine/paracrine production). The activities of IGFs are modulated by a set of specific IGF binding proteins and the IGF type 1 receptor of target tissues. Mitogenic (1) and metabolic properties, such as the uptake of glucose and amino acids (2), incorporation of sulfate into cartilage proteoglycan (3), nucleic acid and protein synthesis, and osmotic and ionic regulation in teleosts (4), have been ascribed to IGF.In the rat and mouse, the direct relationship between increase in the levels of circulating GH and IGF I mRNA has been established in the liver, lung, pancreas, kidney, thymus, spleen, heart, skeletal muscle, testes, and pituitary, but not the uterus and ovary (ref. 5 for review). The effects of GH on IGF I are thought to be due primarily to increased transcription (6) of the IGF I gene rather than effects on the stability of IGF I mRNA. In contrast, it has been suggested that endocrine synthesis of IGF II by the liver is not under the control of GH (7,8) and is regulated by placental lactogen (9) during prenatalThe publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.development. The influence of GH...