EMBRYO MANIPULATION AND GENE TRANSFER IN LIVESTOCK

Abstract

In the past few years significant progress has been made in manipulation of reproduction and in development of genetic engineering techniques which can be applied to animal species. Artificial insemination and embryo transfer are now used widely in the livestock industry. The advent of non-surgical embryo collection and transfer, embryo freezing and splitting along with estrus synchronization has allowed the industry to move from the laboratory to the farm. Embryo manipulation now involves embryo splitting to produce monozygotic twins, in vitro fertilization, cross-species fertilization, embryo sexing, and chimeric production of tetraparental animals among others. Advances in recombinant DNA, plasmid construction and embryo manipulation technologies allow the production of genetically engineered animals. The application of recombinant DNA technology involves the isolation and manipulation of desired genes which have potential for significant changes in productivity in genetically engineered livestock. Recombinant DNA constructs involve the coupling of promoter, enhancer, regulatory and structural DNA sequences to form a "fusion gene" which can then be multiplied, purified, assayed and expressed in cell culture prior to being introduced into an animal genome. Such DNA gene constructs are readily available for many human and mouse genes. However, they are not readily available for livestock species because the detailed molecular biology has not yet been established in these species. Gene transfer offers a powerful new tool in animal research. Transfer of genes into the bovine genome has been accomplished. However, successful directed expression of these incorporated genes has not been achieved to date. New combinations of fusion genes may be an effective way of producing transgenic domestic animals which show controlled expression of the desired genes. Embryo manipulation and genetic engineering in livestock species is moving rapidly. The problems being addressed at present in numerous laboratories will result in enhanced livestock production in the not too distant future. Key words: Embryo transfer, embryo manipulation, transgenic livestock, genetic engineering, gene transfer, monozygotic twins