Embryonic stem cells as tools for investigating human development
Human embryonic stem cells (hESCs) are pluripotent stem cells derived from the inner cell mass of human embryos in the blastocysts stage of development. They show an unlimited capacity to self-renew in culture systems both in vivo and in vitro. Thanks to these two outshining characteristics, hESCs have served as powerful tools for studying human development (1).
Pluripotency and broad differentiation potential of hESCs:
Human embryonic stem cells are unique in their unlimited life span and their broad developmental potential. They are pluripotent and can differentiate into all types of cells. The expression of genes, such as OCT4, Rex1 and Nanog which are commonly expressed in undifferentiated cells demonstrates their pluripotency and their differentiation potential. In addition, they exhibit the activity of several enzymes such as telomerases and alkaline phosphatases (2,3).
In vitro cultivation of hESCs and their expansion in animal models:
When maintained in vitro as suspension cultures, hESCs tend to aggregate and form spheres that are dynamic in nature. While growing, differentiation can take place leading to the generation of different cell types such as the ones present in the heart, bones, muscles, and the liver. During differentiation, cells undergo morphological changes and acquire the expression of specific marker genes (4).
When hESCs are inoculated into animal models, nonmalignant tumours called teratomas are formed, which contain various cell types including muscle cells, epithelial cells, cells of the neuroectoderm and of the bone tissue (4).
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- Reubinoff BE, Pera MF, Fong CY, Trounson A, Bongso A 2000 Embryonic stem cell lines from human blastocysts: somatic differentiation in vitro. Nat Biotechnol 18: 399–404
- Thomson JA, Odorico JS 2000 Human embryonic stem cell and embryonic germ cell lines. Trends Biotechnol 18: 53–57
- Itskovitz-Eldor J, Schuldiner M, Karsenti D, Eden A, Yanuka O, Amit M, Soreq H, Benvenisty N 2000 Differentiation of human embryonic stem cells into embryoid bodies compromising the three embryonic germ layers. Mol Med 6: 88–95