الفهرس 
DEDICATION
Aim of the EssayOnly 14 pages are availabe for public view
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Abstract
Stem cells are primitive cells that have the capacity of self-renewal and differentiation into multiple cell types. They are classified, according to their origin, into four types: 1. Embryonic stem cells--- present in the inner cell mass of blastocyst. 2. Fetal stem cells--- present in fetal tissue as placenta and umbilical cord. 3. Adult stem cells--- present in adult tissues. 4. Induced pluripotent stem cells--- which are artificially-derived cells generated by reprogramming of somatic cells to acquire ESC-like properties. The ethical controversies facing the use of human embryos as a source of ESCs and the problem of tissue rejection following transplantation in recipient patients, in addition to the difficulty in isolation of adult stem cells at sufficient purity and quantity push scientists to try to generate pluripotent stem cells from adult somatic cells through reprogramming. Strategies of somatic cell reprogramming include: 1. Somatic cell nuclear transfer, including the transfer of somatic cell nucleus into enucleated oocyte. Exposure of the transferred nucleus to factors in the cytoplasm of the oocyte returns it to a pluripotent state. 2. Cell fusion, including fusion of a somatic cell with a pluripotent cell, like ESC and ECC. The resulting hybrids feature many characteristics of ESCs. 3. Culture-induced reprogramming, including generation of pluripotent stem cells during the course of culture of testes cells. 4. Direct reprogramming of somatic cells by inducing forced expression of certain stemness genes producing iPSCs.