Utilization of transgenic animals for applied biology

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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