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Stem cells (SC)

Stem cells (SC) are unique cells present in multicellular organisms that, unlike other cells, have the potential to differentiate into specialized cells as well as to divide via mitosis to produce more SC. Embryonic stem cells (ESC) are present in an embryo which forms from a fertilized egg. ESCs differentiate in three germ layers–ectoderm, endoderm, and mesoderm–which give rise to all the tissues and organs present in an organism. Adult SC (somatic SC) are undifferentiated cells found in differentiated tissue or organ. The maintenance and repair of many adult tissues are ensured by adult SC, which resides at the top of the cellular hierarchy of these tissues. While ESCs are defined by their origin, the origin of adult SC is still under debate. A progenitor cell is a cell that has a potential to differentiate into a specific type of cell, however, compared to a SC it is more differentiated and does not have a potential to become any cell of the living organism. Unlike SC, progenitor cells cannot replicate indefinitely, but only a limited number of times. Adult (differentiated) cells can be genetically reprogrammed to acquire SC-like properties by forced expression of genes and factors important for maintaining the defining properties of embryonic SC. Those cells are called induced pluripotent stem cells (iPSCs) and meet the defining criteria for pluripotent SC. However, it is still not known if sESCs and iPSCs differ in a clinically significant way (Yamanaka, 2012). Cancer stem cells (CSC) are cells found in certain types of cancer that possess characteristics of normal SCs. Through the process of self-renewal and differentiation CSCs can gicancer sample and are therefore considered tumorigenic. CSCs are relatively quiescent and hard to target via commonly used anticancer therapies. They continue to reside inside the body after the therapeutic treatment and pose a source of cancer cells that causes relapse as well as metastasis (Beck and Blanpain, 2013). So far, CSC has been confirmed to be present in leukemia, melanoma, multiple myeloma as well as brain, breast, colon, ovary, pancreas, and prostate cancer (Kreso and Dick, 2014).ve rise to all the cell types present in a certain

adult stem cells, cancer stem cells, embrionic stem cells, progenitor stem cells, stem cells

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