Production of transgenic sheep with growth-regulating genes.

Pronuclei of fertilized sheep ova were injected with fusion genes consisting of the mouse metallothionein-I promotor/regulator ligated to either the structural gene for bovine growth hormone (mMTbGH) or to a minigene for human growth hormone-releasing factor (mMThGRF). From a total of 842 sheep ova injected with mMTbGH and transferred into recipient ewes, 47 lambs were born. Two of the lambs were transgenic with mMTbGH, and both had bGH mRNA present in liver, kidney, and gut. In one lamb, plasma growth hormone was as high as 700 ng/ml. From a total of 435 sheep ova injected with mMThGRF and transferred to recipients, 54 lambs were born and 9 fetuses were collected. Nine of the 63 had integrated the mMThGRF gene. One of the nine had high concentrations of immunoassayable hGRF in its plasma and high variable plasma concentrations of ovine growth hormone. The lamb that expressed the hGRF gene did not release GH in response to an hGRF challenge. Four of five fetal offspring of a nonexpressing mMThGRF transgenic ram also contained the mMThGRF gene and, like the sire, failed to express the gene as determined by either liver hGRF mRNA or by plasma hGRF. Growth of the single transgenic lamb expressing hGRF was similar to control lambs. These studies demonstrate efficient introduction of genes into the sheep genome and indicate that transgenes are expressed and heritable.