Embryonic stem (ES) cell
ES cells have been established produced from the inner core of the blastocyst. They preserve their undifferentiated state and normal nuclei during subculture, however, they are then capable of differentiation into any kind of tissues. Proliferated ES cells first become stem cells (such as neuronal stem cells, muscle stem cells, vascular endothelial stem cells and hematopoietic stem cells) according to the specific culture conditions, and then differentiate into neurons, muscle cells, vascular endothelial cells and blood cells. However, unlike the fertilized egg, a cluster of ES cells cannot independently develop into a human being.
It is expected that ES cells will contribute to biomedical research and medical treatment. In the field of research, they can be used to locate various molecules and genes engaged in the proliferation and differentiation of many cell types. In the field of medicine, they are expected to be useful in the development of artificial organs to be transplanted and in cell transplantation. The contribution of ES cell research to organ transplantation is expected to be beneficial in blood transfusion as well as to advance treatment of Alzheimer’s disease, myocardial infarct, angiopathy, and muscular dystrophy.
The introduction of genes into ES cells can be easily carried out for purposes such as the removal of gene function in cells, the introduction of mutation and gene replacement. This technique also makes it possible to create a knockout animal which destroys the function of a specific gene. Future research will enable us to transplant a patient’s nuclei into ES cells to create an organ dedicated for that specific patient. Research into ES cell strains is more advanced in mice than in humans, however, both human and animal ES cell strains have already been established. Since it is no longer merely a dream to create human clones using ES cell techniques, ethical issues are currently under discussion.
Fig.1
Application of ES cell research in the creation of chimera animals
Chimeras, animals whose cells are derived both from the original embryos and from mutation-introduced ES cells, can be created by manipulating genes to introduce a mutation into ES cells and then returning the ES cells to the early embryos. The target mutant can be obtained by selecting animals having germ cells derived from the ES cells. Knockout animals which delete the function of a specific gene can also be created using the same technique.
Subculture of ES cells preserving the undifferentiated state
Strains of ES cells have been created by removing and cultivating the inner core of the blastocyst from the fertilized ova. Mouse ES cells are now available commercially. Subculture of ES cells requires feeder cells, which release Leukemia Inhibitory Factor (LIF), the factor required to preserve the ES cells in their undifferentiated state. If LIF is added directly into the culture medium, the ES cells can be preserved in an undifferentiated state without the feeder cells.
