User:L!ttleW0lf/Reprogramming
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History
The first person to successfully demonstrate reprogramming was John Gurdon, who in 1962 demonstrated that differentiated somatic cells could be reprogrammed back into an embryonic state when he managed to obtain swimming tadpoles following the transfer of differentiated intestinal epithelial cells into enucleated frog eggs.[1] For this achievement he received the 2012 Nobel Prize in Medicine alongside Shinya Yamanaka.[2] Yamanaka was the first to demonstrate (in 2006) that this somatic cell nuclear transfer or oocyte-based reprogramming process (see below), that Gurdon discovered, could be recapitulated (in mice) by defined factors (Oct4, Sox2, Klf4, and c-Myc) to generate induced pluripotent stem cells (iPSCs).[3] Other combinations of genes have also been used, including LIN25 and Homeobox protein NANOG[4].[5]
Phases of reprogramming into iPSC
With the discovery that cell fate could be altered, the question of what progression of events occur to signify a cell reprogramming. As the final product of iPSC reprogramming was similar in morphology, proliferation, gene expression, pluripotency, and telomerase activity was way to determine what phase of reprogramming was needed.[6] Reprogramming is defined into three phase: initiation, maturation, and stabilization.[7]
Initiation
The initiation phase is associated with the downregulation of cell type specific genes and the upregulation of pluripotent genes.[7] As the cells move towards pluripotency, the Telomerase activity is reactivated to extend telomeres. The cell morphology can directly affect the reprogramming process as the cell is modifying itself to prepare for the gene expression of pluripotency.[8] The main indicator that the initiation phase has completed is that the first genes associated with pluripotency are expressed. This includes the expression of Oct-4 or Homeobox protein NANOG, while undergoing a Mesenchymal–epithelial transition (MET), and the loss of Apoptosis and Senescence.[9]
If the cell is directly reprogrammed from one somatic cell to another, the genes associated with each cell type begin to be upregulated and downregulated accordingly.[7] This can either occur through direct cell reprogramming or creating a intermediate, such as a iPSC, and differentiating into the desired cell type.[9]
The initiation phase is completed through one of three pathways: nuclear transfer, cell fusion, or defined factors (MicroRNA, Transcription factor, epigenetic markers, and other small molecules).[9]
Somatic cell nuclear transfer
An oocyte can reprogram an adult nucleus into an embryonic state after somatic cell nuclear transfer, so that a new organism can be developed from such cell.[10]
Reprogramming is distinct from development of a somatic epitype,[11] as somatic epitypes can potentially be altered after an organism has left the developmental stage of life.[12] During somatic cell nuclear transfer, the oocyte turns off tissue specific genes in the Somatic cell nucleus and turns back on embryonic specific genes. This process has been shown through cloning, as seen through John Gurdon with the tadpoles[1] and Dolly (sheep).[13] Notably, these events have shown that cell fate is a reversible process.
Cell fusion
Cell fusion is used to create a multi nucleated cell called a Heterokaryon.[9] The fused cells allow for otherwise silenced genes to become reactivated and expressive. As the genes are reactivated, the cells can re-differentiate. There are instances where transcriptional factors, such as the Yamanaka factors, are still needed to aid in heterokaryon cell reprogramming.[14]
Defined factors
Unlike nuclear transfer and cell fusion, defined factors do not require a full genome, but only reprogramming factors. These reprogramming factors include MicroRNA, Transcription factor, epigenetic markers, and other small molecules.[9] The original transcription factors, that lead to iPSC development, discovered by Yamanaka include Oct4, Sox2, Klf4, and c-Myc (OSKM factors).[3][6] Although the OSKM factors have been shown to induce and aid in pluripotency, other transcription factors such as Homeobox protein NANOG[15], LIN25[4], TRA-1-60[16], and C/EBPα[17]. The use of MicroRNA and other small molecule-driven processes has been utilized as a means of increasing the efficiency of the differentiation from somatic cells to pluripotency.[9]
Maturation
The start of the maturation phase is at the end of the initiation phase, where the first pluripotent genes are expressed.[7] The cell is preparing itself to be independent from the transgenes, or defined factors, that started the reprogramming process. The first genes to be detected in iPSCs are Oct4, Homeobox protein NANOG, and Esrrb while followed later by Sox2.[9] In the later stages of maturation, transgene silencing marks the start of the cell becoming independent from the induced transcription factors. Once the cell is indipendent, the maturation phase ends and the stabilization phase begins.
As reprogramming efficiency has been seen to be a variable and low efficiency process, not all the cells complete the maturation phase and achieve pluripotency.[17] Some cells that undergo reprogramming still under apoptosis at the beginning of the maturation stage from oxidative stress brought on by the stresses of gene expression change. The use of microRNA, proteins, and different combinations of the OSKM factors have started to lead towards a higher efficiency rate of reprogramming.
Stabilization
The stabilization phase is the processes in the cell that occur after the cell reaches pluripotency. One genetic marker is the expression of Sox2 and X chromosome reactivation, while epigenetic changes include the telomerase extending the Telomeres[4] and the epigenetic memory of the cell is lost.[7] The epigenetic memory of a cell is reset by the changes in DNA methylation[18], using Activation-induced cytidine deaminase (AID), TET enzymes (TET), and DNA methyltransferase (DMNTs), starting in the maturation phase and into the stabilization stage.[7] Once the epigenetic memory of the cell is lost, the possibility of differentiation into the three germ layers is achieved.[6]
In cell culture systems
Reprogramming can also be induced artificially through the introduction of exogenous factors, usually transcription factors. In this context, it often refers to the creation of induced pluripotent stem cells from mature cells such as adult fibroblasts. This allows the production of stem cells for biomedical research, such as research into stem cell therapies, without the use of embryos. It is carried out by the transfection of stem-cell associated genes into mature cells using viral vectors such as retroviruses.
Transcription factors
OSKM
NANOG
C/EBPα
Variability
The properties of cells obtained after reprogramming can vary significantly, in particular among iPSCs.[19] Factors leading to variation in the performance of reprogramming and functional features of end products include genetic background, tissue source, reprogramming factor stoichiometry and stressors related to cell culture.[19]
include different combinations of transcriptional factors, c/ebp/ etc
Direct cell reprogramming
B cells to T cells
B cells into Macrophage
B cells to Erythroid
References
- ^ a b Gurdon JB (December 1962). "The developmental capacity of nuclei taken from intestinal epithelium cells of feeding tadpoles". Journal of Embryology and Experimental Morphology. 10: 622–40. PMID 13951335.
- ^ "The Nobel Prize in Physiology or Medicine – 2012 Press Release". Nobel Media AB. 8 October 2012.
- ^ a b Takahashi K, Yamanaka S (August 2006). "Induction of pluripotent stem cells from mouse embryonic and adult fibroblast cultures by defined factors" (PDF). Cell. 126 (4): 663–76. doi:10.1016/j.cell.2006.07.024. PMID 16904174. S2CID 1565219.
- ^ a b c Magalhães, João Pedro de; Ocampo, Alejandro (2022-06-01). "Cellular reprogramming and the rise of rejuvenation biotech". Trends in Biotechnology. 40 (6): 639–642. doi:10.1016/j.tibtech.2022.01.011. ISSN 0167-7799. PMID 35190201.
- ^ Baker M (2007-12-06). "Adult cells reprogrammed to pluripotency, without tumors". Nature Reports Stem Cells. doi:10.1038/stemcells.2007.124.
- ^ a b c Takahashi, Kazutoshi; Tanabe, Koji; Ohnuki, Mari; Narita, Megumi; Ichisaka, Tomoko; Tomoda, Kiichiro; Yamanaka, Shinya (2007-11-30). "Induction of Pluripotent Stem Cells from Adult Human Fibroblasts by Defined Factors". Cell. 131 (5): 861–872. doi:10.1016/j.cell.2007.11.019. ISSN 0092-8674. PMID 18035408.
- ^ a b c d e f David, Laurent; Polo, Jose M. (2014-05-01). "Phases of reprogramming". Stem Cell Research. 12 (3): 754–761. doi:10.1016/j.scr.2014.03.007. ISSN 1873-5061.
- ^ Downing, Timothy L.; Soto, Jennifer; Morez, Constant; Houssin, Timothee; Fritz, Ashley; Yuan, Falei; Chu, Julia; Patel, Shyam; Schaffer, David V.; Li, Song (2013-12). "Biophysical regulation of epigenetic state and cell reprogramming". Nature Materials. 12 (12): 1154–1162. doi:10.1038/nmat3777. ISSN 1476-1122.
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{{cite journal}}: CS1 maint: PMC format (link) CS1 maint: unflagged free DOI (link) - ^ Hochedlinger K, Jaenisch R (June 2006). "Nuclear reprogramming and pluripotency". Nature. 441 (7097): 1061–7. Bibcode:2006Natur.441.1061H. doi:10.1038/nature04955. PMID 16810240. S2CID 4304218.
- ^ Lahiri DK, Maloney B (2006). "Genes are not our destiny: the somatic epitype bridges between the genotype and the phenotype". Nature Reviews Neuroscience. 7 (12): 976. doi:10.1038/nrn2022-c1.
- ^ Mathers JC (June 2006). "Nutritional modulation of ageing: genomic and epigenetic approaches". Mechanisms of Ageing and Development. 127 (6): 584–9. doi:10.1016/j.mad.2006.01.018. PMID 16513160. S2CID 9187848.
- ^ Wilmut, I.; Schnieke, A. E.; McWhir, J.; Kind, A. J.; Campbell, K. H. S. (1997-02). "Viable offspring derived from fetal and adult mammalian cells". Nature. 385 (6619): 810–813. doi:10.1038/385810a0. ISSN 0028-0836.
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{{cite journal}}: Check date values in:|date=(help) - ^ a b Srivastava, Deepak; DeWitt, Natalie (2016-09). "In Vivo Cellular Reprogramming: The Next Generation". Cell. 166 (6): 1386–1396. doi:10.1016/j.cell.2016.08.055. PMC 6234007. PMID 27610565.
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