Advances in reprogramming somatic cells to induced pluripotent stem cells

Abstract

Traditionally, nuclear reprogramming of cells has been performed by transferring somatic cell nuclei into oocytes, by combining somatic and pluripotent cells together through cell fusion and through genetic integration of factors through somatic cell chromatin. All of these techniques changes gene expression which further leads to a change in cell fate. Here we discuss recent advances in generating induced pluripotent stem cells, different reprogramming methods and clinical applications of iPS cells. Viral vectors have been used to transfer transcription factors (Oct4, Sox2, c-myc, Klf4, and nanog) to induce reprogramming of mouse fibroblasts, neural stem cells, neural progenitor cells, keratinocytes, B lymphocytes and meningeal membrane cells towards pluripotency. Human fibroblasts, neural cells, blood and keratinocytes have also been reprogrammed towards pluripotency. In this review we have discussed the use of viral vectors for reprogramming both animal and human stem cells. Currently, many studies are also involved in finding alternatives to using viral vectors carrying transcription factors for reprogramming cells. These include using plasmid transfection, piggyback transposon system and piggyback transposon system combined with a non viral vector system. Applications of these techniques have been discussed in detail including its advantages and disadvantages. Finally, current clinical applications of induced pluripotent stem cells and its limitations have also been reviewed. Thus, this review is a summary of current research advances in reprogramming cells into induced pluripotent stem cells.

Figure 1

Diagram represents different techniques to generate pluripotent stem cells. (a) Somatic Cell Nuclear Transfer: Nuclear DNA isolated from a somatic donor cell is introduced into an enucleated oocyte (oocyte which has its nucleus removed) to form a pre-developed embryo which is cultured until full development. The developed embryo is implanted into a foster mother ultimately resulting in cloned neonates, (b) Cell Fusion: Somatic cells and pluripotent embryonic stem cells go through cell fusion to generate reprogrammed cells. The cytoplasm of embryonic stem cells contains reprogramming factors which can alter the epigenetic state of a somatic cell into a pluripotent cell being fused with a somatic cell, (c) Reprogramming Through Cell Extracts: Cell extracts obtained from pluripotent stem cells are inserted into somatic cells which leads to nuclear reprogramming to generate a pluripotent stem cell and (d) Direct Reprogramming: A selection of transcription factors are introduced into somatic cells through viral or non viral vector sources to generate pluripotent stem cells.