1. Pluripotent stem cells:

 

Pluripotent stem cells are cells that can give rise to all types in all the three germ layers (Ectoderm, Endoderm, Mesoderm) but doesn’t have the ability to regenerate the placenta. These are also known as late embryonic cells.

There are two types of Pluripotent stem cells: Embryonic stem cells (Late ESCs) and Induced Pluripotent stem cells (iPSCs)

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(i) Embryonic stem cells:

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These were first isolated in 1981 from the ICM of mouse blastocysts. They found out that the epiblast cells of Embryonic Day, E5.5 have homology with Embryonic Carcinoma cells and are most capable of producing Pluripotent cells in culture. E5.5 is the early implantation stage where the coital plug arises and yields the most number of Pluripotent stem cells in isolation. These were grown on a layer of feeder cells, consisting of fibroblasts and Pluripotent cells were successfully isolated.

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(ii) Induced Pluripotent stem cells (iPSCs): 

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As isolation of Pluripotent stem cells is expensive, difficult, and raises a lot of ethical issues, in 2006, Yamanaka devised a method to induce pluripotency into cells, and hence, a new type of pluripotent stem cells was found. Yamanaka and his colleagues used a cocktail of 4 transcription factors, Oct3/4, Klf4, Sox2, and c-Myc, and grew mouse fibroblast cells on it over an STO feeder layer. They saw ESC-like characteristics in these cells and termed them as induced Pluripotent stem cells. This was breakthrough research in the field of stem cells and Yamanaka was given the noble prize in 2012 for medicine and physiology.

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2. Multipotent Stem cells

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Multipotent stem cells were the first types of stem cells to be isolated. Till and McCulloch in the 1960s were the first ones to isolate Multipotent stem cells. They discovered that Bone marrow and thymus cells from mice were able to regenerate the full hematopoietic system in the immunocompromised irradiated mice. They found the same results when the same transplant was conducted from the primary irradiated mice to another irradiated mouse. This process is known as serial transplantation. The cells responsible for this were found out to be hematopoietic stem cells.

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This was the first discovery of stem cells and also the first to prove that bone marrow transplantation can be used in medical sciences. Unlike the Pluripotent stems, multipotent stem cells are lineage-specific and are only able to give cells of a particular lineage e.g., NSCs will give rise to cells to the neural lineage, and HSCs will give rise to hematopoietic cells.