The Development of Sheep Expressing Growth Promoting Transgenes

The first successful attempts to transfer foreign DNA into mice (Gordone, et al, 1980) were rapidly followed by a number of reports demonstrating that foreign DNA, or transgenes, can be permanently incorporated into an animal’s genome (Costantini and Lacy, 1981; E. Wagner, et al, 1981; T. Wagner, et al., 1981). Once incorporated, transgenes are stable and can be transmitted to an animal’s progeny in the course of normal breeding. The potential for the application of transgenic technology to alter animals used in agriculture was further indicated by Palmiter and his colleagues (1982,1983). These workers produced mice transgenic with a rat growth hormone (rGH) gene that was under the control of the mouse metallothionein I (MT) gene promoter, thus directing the production of GH in the liver rather than the anterior pituitary. The resulting transgenic mice that expressed this transgene grew to approximately 1.5 to 2 times as large as non-transgenic littermates. Thus, they established that the alteration of the pattern of expression of a gene, or the expression of a foreign gene, could result in a marked change in a quantitative trait like body growth. The control of growth, feed efficiency, reproduction, fat deposition and disease resistance are all economically important traits in animal agriculture. At this point in 1982, laboratories at the USDA/ARS facility at Beltsville, Maryland (C.E.R. Jr.) and the CSIRO, Division of Animal Production in Sydney, Australia (J.D.M.) began experiments designed to transfer growth hormone transgenes into sheep. The goals of both groups were to determine 1—if growth hormone transgenic sheep were more feed efficient, i.e., produced more muscle per unit of food consumed, 2-contained less fat and 3-grew more rapidly than non-transgenic controls, as such modifications would be advantageous to producers. In this paper we will discuss the experimental work concerned with producing growth hormone transJAMES D. MURRAY