From Cell to Production

Technical Challenges of Cloning Pigs for BioMedical Research

Somatic Cell Nuclear Transfer in Mammals

SATACs and Transgenesis

Concerns About Gene Transfer and Nuclear Transfer in Domestic Animals

Prospects and Hurdles in Optimizing the Vascular Support of Engineered Tissues

ES Cells Make Neurons in a Dish

Nuclear Transfer and Gene Targeting in Domestic Animals: Bioreactors of the Future

Application of Nuclear Transfer Technology in the Generation of Pigs for Xenetransplantation

Genomics: Delivering Cell Culture Systems for Tissue Therapy

Nuclear Transfer Technology

Gene Targeting in Domestic Species: Challenges and Opportunities

Homologous Recombination and Genetic Engineering of Transgenic Recombinant Animals

Nuclear Transplantation in the Cow: Future Challenges

Enhancing Transgenics through Cloning

ES Cells Offer is a Power Tool for Understanding the Genetic Control of Tissue Development and for Screening Potential Therapeutic Drugs

Human Germline Engineering -- The Prospects for Commercial Development

Mammalian Artificial Chromosomes for Animal Transgenesis

Understanding Developmental Abnormalities in Offspring Produced by Nuclear Transplantation

Role of Cell Cycle

Cloning and Other Reproductive Technologies for Application in Transgenics

CELL CULTURING TECHNOLOGY AS A MAJOR HURDLE IN THE COMMERCIALIZATION OF GENETICALLY ALTERED ANIMALS

Participant:

Linda Yaswen-Corkery
Metamorphix

Animal biotechnology presents considerable potential benefits to the world of agriculture. Three current anticipated uses for genetically engineered animals include: xenotransplantation, pharmaceutical drug production, and enhanced livestock production through selective genetic traits. The need for commercialization of this technology is perhaps best illustrated by the belief that conventional technologies are not expected to increase the agricultural productivity level to that required by the world's ever-growing population. Transgenic animals can contribute greatly to the task of feeding the estimated three billion people who are to be born within the next three decades. Surmounting technological hurdles will serve to lower production investment costs, causing the development of useful products from animal biotechnology to greatly expand.

Some major barriers affecting the availability of transgenic animals for commercialization are: inadequate ability to culture embryos to maintain totipotency, inability to maintain Embryonic Stem (ES) and Primordial Germ (PG) cells in culture long enough to allow for extensive genetic selections, low survival ratio of developmentally competent transplanted embryos, and the high cost of maintaining donor and recipient populations for research development. Additionally, the long gestation and maturation time, in comparison to mice, has impeded our ability to become proficient in cell harvesting, culturing, and transplanting of genetically altered embryos.

Much of our information regarding embryo culturing and development is derived from studies of mice. Studies of embryos from domestic animals have established that their physiology differs dramatically from that of the mouse. Significant delays in pre-implantation and pre-attachment of sheep and cattle, as opposed to mice, may explain some of the apparent differences in culture requirements for these embryos (King, G. J. and Thatcher, W. (1993) Pregnancy. In Reproduction in Domestic Animals, edited by G. J. King, pp. 229-269. Amsterdam: Elsevier). Dynamic media conditions which follow the developmental requirements of the changing embryo need to be further established. Thus, the research efforts aimed at further characterizing the components within the reproductive tract and elucidating their functions and complex interactions should be considered a major priority for the advancement of transgenic animal technology.

Culture conditions of genetically altered cell lines need to be advanced in parallel with the embryo culturing effort to increase the window of time in which cultured cells can be manipulated. This would allow for the selection of precise genetic modifications (knockouts, insertions, and modifications to regulatory regions), serving to eliminate problems which result when genetic material is randomly inserted into the genome. Additional time in culture would also make dual selection techniques possible, which could be employed to decrease or eliminate foreign genetic material remaining within the genetically altered animals. This could lower regulatory testing costs and generate greater public acceptance. The ability to perform multiple selections in culture may also allow for product protection of some altered livestock, making financial commitments from companies more forthcoming.