Copyright ©2013 Baishideng Publishing Group Co.
World J Gastroenterol. Jun 14, 2013; 19(22): 3385-3396
Published online Jun 14, 2013. doi: 10.3748/wjg.v19.i22.3385
Table 1 New approaches to reprogramming of differentiated cells to a pluripotent state
MethodResults of reprogrammingDrawbacksRef.
Transfer of the nucleus from a somatic cell to an enucleated oocyteThe somatic cell nucleus is reprogrammed in the oocyte, and a whole organism develops as a result. Patient-specific hESCs can be derivedLow efficiency. Developmental abnormalities in cloned animals. Ethical and legal restrictions[24-28]
Fusion of ESCs with differentiated cellsHybrids of differentiated cells and ESCs display all properties of pluripotent cellsCell hybrids lack a normal diploid chromosome set[29,30]
Reprogramming of somatic cells to a pluripotent state can be generated by the ectopic expression of 4 transcription factors, Oct4, Klf4, Sox2 and c-MycSomatic cells regain a pluripotent state and become similar in properties to ESCsLow efficiency of iPSC derivation. Viral integration. Tumor formation[7]
Table 2 Various induction methods to generate induced pluripotent stem cells
Retroviral vectorsHigh efficiencyGenome integration, dividing target cells needed[7-9,32,41,42]
Lentiviral vectorsHigh efficiency, target cells need not be dividingGenome integration[47-49]
Lentiviral vectors with Cre/LoxHigh efficiencyMinimize genomic integration[43,44]
Piggyback transposonPrecise deletion is possibleMinimize genomic integration, laborious[45,46]
Viral vectorsNo genome integrationLow efficiency[34-37]
Adenoviral vectors
Sendai vectors
DNA vectors
Plasmid vectors
Episomal vectors
Minicircle vectors
Protein transductionNo genome integrationLow efficiency[38]
Small moleculesNo genetic modificationLow efficiency[39]
Synthetic mRNANo genetic modification, high efficiencyMultiple rounds of transfection are needed[40]
Table 3 Role of reprogramming factors for induced pluripotent stem cell generation
Reprogramming factorsDescriptionFunctionRef.
Oct4Octamer binding transcription factor 4This transcription factor plays a role in embryonic development, especially during early embryogenesis, and it is necessary for embryonic stem cell pluripotency[7]
Sox2SRY box 2In embryonic stem cells, Sox2 and Oct3/4 often co-occupy target genes, including own promoters. These proteins cooperate regulatory feedback loops to maintain pluripotency[60]
Klf4Kruppel-like factor 4This transcription factor plays a role in upregulation of pluripotency gene Nanog and the modification of chromatin structure to facilitate the binding of Oct3/4 and Sox2 to their sequences. Klf4 itself is an oncogenic factor. This gene is over expressed in a variety of tumor types associated with advanced cancer[61-63]
c-MycProto oncogene proteinAn oncogene that induces global histone acetylation, allowing Oct3/4 and Sox2 to bind to their specific target loci[60,63]
NanogHomeo box transcription factorA transcription factor critically involved with self-renewal of undifferentiated embryonic stem cells[64]
Lin28RNA binding protein Lin28The Lin28 gene codes for an RNA-binding protein that selectively blocks the processing of microRNAs of the let-7 family, and possibly certain other microRNAs in ESCs, to prevent their differentiation[65,66]
Table 4 Differentiation protocols for induced pluripotent stem cell-derived hepatocytes
Ref.SpeciesDifferentiation protocolRemarks
Sullivan et al[78]HumanActivin A, Wnt3a (3 d), Activin A (2 d), DMSO (3 d), HGF, OSM (6 d)Generated functional hepatocyte-like cells from human-iPSCs
Song et al[79]HumanActivin A (3 d), FGF4, BMP-2 (4 d), HGF, KGF (6 d), OSM, Dex (5 d) then OSM, Dex, N2B27 (3 d)iPSCs had fewer expressed liver-enriched genes compared with human hepatocytes
Si-Tayeb et al[80]HumanActivin A (5 d), bFGF, BMP-4 (5 d), HGF (5 d), OSM (5 d)Transplanted hepatocyte-like cells into the lobe of newborn mice and demonstrated homing of donor cells
Liu et al[81]HumanActivin A (5 d), FGF4, HGF (5 d ), Single Quotes (lonza), FGF4, HGF, OSM, Dex (10 d)Human hepatocyte-derived iPSCs are able to differentiate into functional hepatocytes
Takata et al[82]HumanActivin A ( 3 d), HGF (5 d), OSM (5 d)Generated hepatocyte-like cells from iPSCs using three growth factors in a short time
Gai et al[83]MouseActivin A, Wnt3 (6 d), bFGF, DMSO (3 d), HGF, DMSO (9 d), HGF, OSM, DMSO (7 d)Generated hepatocytes from iPSCs
Iwamuro et al[84]MouseActivin A, bFGF (3 d), HGF (5 d)Generated hepatocyte-like cells from iPSCs
Table 5 Direct conversion approaches for specific cell types
Ref.Key factorsDirect converted cell type
Vierbuchen et al[109]Brn2, Ascl1, and Myt1lTransdifferentiated mouse fibroblasts into functional neuronal cells
Ieda et al[110]Gata4, Mef2c, and Tbx5Transdifferentiated mouse dermal fibroblasts into cardiomyocyte-like cells
Szabo et al[111]Oct4Transdifferentiated human fibroblast cells into hematopoietic progenitors
Huang et al[112]Gata4, Hnf1α and Foxa3, and inactivation of p19ArfTransdifferentiated mouse tail-tip fibroblasts into hepatocyte-like cell