Porcine growth hormone gene expression from viral promoters in transgenic swine

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Abstract
The production of porcine growth hormone (pGH) from novel expression vectors containing the promoter/enhancer elements of the Moloney murine leukemia virus (MLV) LTR or the human cytomegalovirus (CMV) immediate early gene was examined in transgenic swine. Both fusion genes resulted in elevated levels of serum pGH, elevation of insulin‐like growth factor 1 (IGF‐1), and a pronounced decrease in carcass fat deposition. The two viral promoter/enhancer elements were constitutively active in the transgenic swine throughout the life of the animals. In individual swine, the CMV‐pGH transgene was expressed predominantly in the pancreas while the MLV‐pGH transgene was expressed in a wide variety of tissues. These swine were infertile, had insulin resistance, and demonstrated an accelerated form of osteochondritis dissicans. Our results show that excess pGH produces a phenotype identical to that seen in swine expressing heterologous growth hormones, and provides a baseline for assessing the overall efficiency of producing transgenic swine. Furthermore, our data suggests that unregulated pGH production, even at 15 times normal levels and independent of the tissue source, has adverse effects that outweigh the desired reduction in carcass fat deposition in transgenic swine.