What is a stem cell?
1 Answer
Here is the definition
Explanation:
Stem cells by definition are cells that can proliferate extensively over several generations and differentiate into other cell types.
Explanation:
There are embryonic and adult sources of stem cells. Stem cells can also be 'made' in the laboratory by reprogramming other cell types to a pluripotent state (iPSCs)
Embryonic stem cells (ESCs) are derived from embryos at the blastocyst stage. In culture, they can self-renew for many population doublings without going into senscence. They can be differentiated into cells of all three germ layers (ectoderm, mesoderm and endoderm). If injected in an animal, embryonic stem cells form a teratoma, which is a mass resembling a tumor containing cells of the three germ layers. Another speciality is that ESCs have the potential to give rise to an entire organism, or at least, if they are put in an empty blastocyst and placed in the uterus of a surrogate mother they would implant and continue to develop.
Adult stem cells exist as a side population in almost all tissues in the body. They are more restricted in their potential for self renewal and multilineage differentiation. Some examples are Hematopoietic Stem Cells from the bone marrow that give rise to all blood cells, Neural Stem Cells present in the subventricular zone (SVZ) and hippocampus of the brain, and Mesenchymal Stem Cells from various sources such as bone marrow, umbilical cord/blood, placenta, adipose tissue and dental pulp.
Induced Pluripotent Stem Cells (iPSCs) are made by reprogramming cells such as skin fibroblasts, by overexpressing certain pluripotency genes such as OCT4, SOX2, Nanog, KLF4, cMyc. They exhibit all the characteristics of ESCs, but literature suggests that they maintain some epigenetic memory of the cells that they used to be.
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