Utilization of transgenic animals for applied biology

自从人类生长激素（hGH）基因被成功地引入小鼠胚胎，产生了“第一只转基因动物”以来，它已被最频繁地用于通过转基因技术生产具有改良特性的农场动物的试验中。然而，在大多数情况下，这些努力都是徒劳的，因为携带hGH基因的动物会出现胚胎发育受阻、生殖功能衰竭、代谢紊乱等，不幸的是，到目前为止还没有获得有希望的结果。为了解决转基因牛生产中存在的问题，本研究进行了以下调查。乳清酸性蛋白（Whey acid protein， WAP）是哺乳动物乳清中主要的乳清蛋白。WAP基因启动子有望调控乳腺特异性结构基因的表达。在本研究中，我们成功培育了携带hGH基因受小鼠WAP基因启动子控制的杂交基因的转基因小鼠和大鼠。2)获得了携带WAP-hGH基因（BDF1）的转基因小鼠与ICR的杂交后代，该后代在小鼠品系中具有较高的产乳能力。经证实，乳汁中分泌有生物活性的生长激素。转基因动物表现出肥胖、糖尿病和不育。组织学检查发现垂体、性腺、肾上腺及乳腺均有异常。雌性转基因小鼠在12周龄后出现乳腺肿瘤，并检测到MMTV、EGF和TNF高表达。转基因小鼠的寿命相当短，可作为衰老研究的有效模型。3)获得了高生长激素系和低生长激素系两种转基因大鼠。前者的特点是血液中生长激素浓度高，后者的特点是血液中生长激素浓度低。高生长激素系转基因大鼠表现为性早熟、巨人症和不育，低生长激素系转基因大鼠表现为性早熟、肥胖和不育。此外，低生长激素系动物也表现出与非胰岛素依赖型糖尿病（NIDD）相似的有趣特征。低生长激素转基因大鼠血清甘油三酯、游离脂肪酸、胆固醇和酮体水平均显著高于正常大鼠。有关转基因大鼠肥胖和NIDD的研究正在进行中。从人肝脏cDNA文库中分离hGH受体基因，构建了金属硫蛋白启动子与hGH受体基因的杂交基因。我们现在正计划生产表达生长激素受体的转基因大鼠，并获得同时表达生长激素及其受体的杂交动物。这些转基因动物将为研究生长激素的作用和转基因技术在农场动物上的应用提供有益的实验模型。少

Since human growth hormone (hGH) gene was successfully introduced into the mouse embryo to produce the 'first transgenic animal", it has been most frequently employed in the trials of producing the farm animals of improved characteristics by means of transgenic techniques. In most cases, however, such efforts were in vain because of an arrest of embryonic development, failure of reproductive function, manifestation of metabolic disorders, etc. in animals carrying hGH gene, and unfortunately no promising results were obtained so far. To resolve these problems accompanying to produce transgenic cattles, the following investigations were undertaken in this study.1)Whey acidic protein (WAP) is a major whey protein in mammalian milk. WAP gene promoter is expected to regulate the mammary gland specific expression of structural genes. In this study, we have successfully generated transgenic mice and rats carrying a hybrid gene in which hGH gene is under the control of mouse WAP gene promoter. … More 2)The hybrid descendants between transgenic mice carrying WAP-hGH gene (BDF1) and ICR,which is known by their higher ability of producing milk among strains of mice, were obtained. It was confirmed that bioactive hGH was secreted in the milk. The transgenic animals showed obesity, diabetes and infertility. By histological examination, interesting abnormalities were found in the pituitary, gonad, adrenal and mammary glands.In female transgenic mice, mammary tumor developed after the age of 12 weeks, in which high expression of MMTV,EGF and TNF were detected. The span of life of the transgenic mice was considerably short and they should be auseful model for the study of aging.3)Two lines of transgenic rats, i.e., high-hGH line and low-hGH line, were produced.The former was characterized by high concentration of hGH in the blood, while the latter was by low concentration of it. Transgenic rats of high-hGH line showed precocious puberty, gigantism and infertility, and those of low-hGH line showed precocious puberty, obesity and infertility.Further, animals of low-hGH line also showed the interesting features similar to those of non-insulin dependent diabetes (NIDD) .Serum levels of triglyceride, free fatty acids, cholesterol, and keton bodies in the low-hGH transgenic rats were significantly higher than those of normal rats.Studies concerning obesity and NIDD in transgenic rats are being performed.hGH receptor gene was isolated from cDNA library for human liver, and a hybrid gene of metallothionein promoter and hGH receptor gene was constructed. We are now planning to produce transgenic rats expressing hGH receptor and to obtain hybrid animals expressing both hGH and its receptor.These transgenic animals would be useful experimental models for the study of GH actions and application of transgenic techniques to the farm animals. Less