Transgenic mice containing a sheep metallothionein 1a-sheep growth hormone fusion gene exhibited low, tissue-specific basal levels of transgene mRNA expression, resulting in slightly elevated levels of circulating growth hormone that did not lead to a detectable increase in growth. After zinc stimulation, high levels of transgene mRNA expression were induced in a number of tissues; these levels correlated with increased levels of circulating growth hormone, resulting in growth increases of up to 1.5 times the levels of controls and unstimulated transgenic mice. After removal of the zinc stimulus, transgene expression and circulating growth hormone concentrations returned to basal levels. Additional evidence from the pattern of developmental expression of the transgene suggests that zinc is the main regulator of this promoter in mice. The demonstrated regulation and low basal level of expression of the sheep metallothionein 1a promoter make it a candidate for use in other mouse transgenic studies and for use in transgenic livestock, in which regulation of expression is essential.

Samples of oviducal fluid were collected daily from sheep with indwelling catheters. Fluid samples taken from both oviducts of 2 sheep for 2 cycles during the middle of the breeding season (April/May) (8 sets of data) were compared with 9 sets of data generated from 2 cycles in 3 sheep later in the breeding season (June/July). Around the period of oestrus, the output of oviducal fluid increased to a peak volume of 1.56 +/- 0.35 ml per day (mean +/- s.d.) compared with a mid-cycle volume of 0.49 +/- 0.29 ml. Later in the breeding season, the flow rates were lower, but showed the same trend (0.91 +/- 0.24 ml at the peak and 0.25 +/- 0.18 ml 7 days later). The total amount of protein secreted by the oviduct each day increased 2-4-fold around the time of oestrus, with higher levels in mid-season ewes. When oviducal fluids were fractionated by SDS electrophoresis, a novel glycoprotein, subunit size of Mr 80-90 000 was identified in samples for 3-6 days of each cycle, coinciding with the period of high fluid flow rate. This protein first appeared in the oviducal fluid on the day of oestrus or the following day and it represented 1 of the 2 major glycoproteins in oviducal fluid as assessed by periodic acid-Schiff (PAS) staining. A PAS-positive protein (Mr 80-90 000) was also detected in fluid taken after oestrus on native highly cross-linked gradient gels after electrophoresis at pH 3.1 but not at pH 8.3. Both gradient gel systems showed an increase in high molecular weight material (Mr greater than 10(6] in fluid taken soon after oestrus.

The glyoxylate cycle, catalysed by two unique enzymes: isocitrate lyase (ICL; EC 4.1.3.1) and malate synthase (MS; EC 4.1.3.2), is necessary for the net conversion of acetate into glucose. This metabolic pathway operates in microorganisms, higher plants and nematodes. Two bacterial genes, encoding ICL and MS, were modified in order to introduce them into the mouse germ line. The ovine metallothionein-Ia (MT-Ia) promoter-ace B gene-ovine growth hormone (GH) gene (3' GH sequence) construct was fused to the ovine, MT-Ia promoter-ace A gene-ovine GH gene (3' GH sequence). Therefore, in this single DNA sequence, both ace A and ace B are under independent MT-Ia promoter control and can be induced by zinc. Transgenic mice were generated by pronuclear microinjection of the ace B-ace A gene construct. We now report the establishment of four mouse lines carying these two transgenes. Studies on the progeny of these lines indicate that one line (No. 91) is expressing both genes at the mRNA and enzyme levels in the liver and intestine, whereas another line (No. 66) has a much lower expression. Both enzyme activities were detected in the liver and intestine at levels up to 25% of those measured in fully derepressed Escherichia coli cells.

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The techniques involved in the transfer of foreign DNA to domestic animals have advanced to the stage where transgenic animals that express foreign genes can be reliably produced, albeit still at low efficiency. This paper reviews the current status of some of the more important areas in agriculture where this technology is being applied. Numerous attempts have been made to modify the growth performance characteristics of domestic animals by the introduction of metallothionein/growth hormone fusion genes. A summary of our work with transgenic sheep is presented. The results demonstrate that the unregulated production of growth hormone in transgenic sheep reduces carcass fat, elevates metabolic rate and heat production, causes skeletal abnormalities and impairs survival. The introduction of new metabolic pathways to domestic animals offers an attractive approach to improved animal productivity. This paper summarises recent results of research directed towards the introduction of a cysteine biosynthetic pathway and the glyoxylate cycle to transgenic sheep. So far, the genes encoding the enzymes have been isolated and expressed both in cells in culture and in transgenic mice. The results of work currently in progress demonstrate that some modification of the fusion genes is required to enhance their expression in transgenic animals.