Embryonic stem cells are born from embryos that are 3 to 5 days old. At this stage, the embryo is called a blastocyst and contains approximately 150 cells. These cells are pluripotent stem cells.
Understanding Stem Cell Origins
Stem cells, with their remarkable ability to develop into various cell types in the body, have two primary sources: embryonic and adult tissues. Understanding the origin of each type is crucial for grasping their potential and limitations.
Embryonic Stem Cells (ESCs)
- Source: ESCs are derived from the inner cell mass of a blastocyst, an early-stage embryo typically 3-5 days post-fertilization. The blastocyst comprises approximately 150 cells.
- Pluripotency: These cells are pluripotent, meaning they possess the extraordinary capacity to differentiate into virtually any cell type in the body, including all cells of the three primary germ layers (ectoderm, mesoderm, and endoderm). They can also divide to create more stem cells.
- Harvesting: The process of obtaining ESCs involves the destruction of the blastocyst, which raises ethical considerations.
Adult Stem Cells (Somatic Stem Cells)
- Source: These stem cells reside within specific tissues and organs throughout the body after development. Examples include bone marrow (hematopoietic stem cells), skin (epidermal stem cells), and the brain (neural stem cells).
- Multipotency: Adult stem cells are generally considered multipotent, meaning they can differentiate into a limited range of cell types that are specific to their tissue of origin. For example, hematopoietic stem cells in the bone marrow can give rise to various blood cell types but not to brain cells.
- Function: Their primary role is to maintain and repair the tissues in which they reside.
Induced Pluripotent Stem Cells (iPSCs)
- Source: These are adult somatic cells (like skin cells or blood cells) that have been genetically reprogrammed to revert to a pluripotent state, similar to embryonic stem cells.
- Reprogramming: The reprogramming process typically involves introducing specific genes (often called "Yamanaka factors") into the adult cells, which then cause them to regain pluripotency.
- Advantages: iPSCs offer a valuable alternative to ESCs, circumventing the ethical concerns associated with embryo destruction and allowing researchers to create patient-specific stem cells for research and potential therapeutic applications.
In summary, while embryonic stem cells originate directly from the early embryo, adult stem cells reside in mature tissues, and iPSCs are created artificially by reprogramming adult cells to regain pluripotency.
