Researchers identified specific genetic sequences in rats that control the production of growth hormone in the pituitary gland of transgenic mice. By inserting different segments of the rat growth hormone gene into mouse embryos, they found that a region of 181 base pairs is crucial for targeting growth hormone expression to the pituitary. This region activates the gene in growth hormone-producing cells and some cells producing other hormones. The study suggests a link between growth hormone, prolactin, and thyroid-stimulating hormone gene activation in the pituitary gland.