n-acetyl-l-cysteine The characteristics or molecular mechani

The characteristics or molecular mechanisms by which mESCs maintain self-renewal or pluripotency have been determined: mESCs have high alkaline phosphatase (AP) activity, form tightly aggregated, three-dimensional colonies, and maintain their pluripotent character by stable expression of core pluripotent transcription factors such as NANOG, OCT4, or SOX2, in response to stimulation of the Janus kinase/Just another kinase (JAK) and signal transducer and activator of transcription3 (STAT3) pathway by leukemia inhibitory factor (LIF) in serum containing medium (Smith et al., 1992; Niwa et al., 2009). More recently, it has been shown that combined treatment with two small molecule inhibitors (named 2i), the mitogen-activated protein kinase/extracellular regulated kinase (MAPK/ERK) kinase inhibitor PD0325901 and the glycogen synthase kinase 3 beta (GSK3ß) inhibitor CHIR99021 (Ying et al., 2008; Marks et al., 2012), maintains the n-acetyl-l-cysteine in an early naive state, called the ‘ground state’, which is characteristic of ESCs. In addition to mESCs, ICM-originated pluripotent stem cells have been established from human (Thomson et al., 1998) or non-human primate (Thomson et al., 1995; Sasaki et al., 2005) cells. Hence, human or primate ESCs have many characteristics similar to mESCs, such as a stable capacity for self-renewal in vitro and the potential to generate derivatives of all three germ layers (Thomson et al., 1998). However, the morphology and cytokine/growth factor dependency that supports self-renewal in human ESCs are quite different from that in mESCs. Human ESCs form flat, two-dimensional colonies, have low trypsin tolerance during passage (Watanabe et al., 2007; Ohgushi et al., 2010), and express the core pluripotency-maintaining transcription factors such as NANOG, OCT4, and SOX2, by activating ERK1/2- and SMAD2/3-mediated signal transduction in response to FGF2 and ActivinA, respectively. Another pluripotent cell line in mice developed from early epiblast cells of a postimplantation E5.5 to E6.5 fetus, which is called epiblast stem cell (EpiSC), is thought to resemble human ESCs more than mESCs (Brons et al., 2007; Tesar et al., 2007; Hayashi and Surani, 2009). Like human ESCs, EpiSCs form large, flat, two-dimensional colonies, and grow upon stimulation by FGF2 and ActivinA (Brons et al., 2007; Tesar et al., 2007; Greber et al., 2010). Activation of ERK1/2 by FGF2 is a key signal transduction pathway that maintains the self-renewal state of human ESCs or EpiSCs, whereas stimulates differentiation of mESCs (Hamazaki et al., 2006; Kunath et al., 2007; Nichols and Smith, 2009). Likewise, the pluripotent character of human ESCs or EpiSCs cannot be maintained in 2i/LIF culture conditions (Guo et al., 2009; Hanna et al., 2010). Based on these different cytokine dependencies, numerous studies have attempted to revert primed human ESCs or mouse EpiSCs to a naive or ground state by changing their growth factor, or cytokine dependency, from FGF2/ActivinA to LIF and/or 2i (Zhou et al., 2010; Hanna et al., 2010). Murine induced pluripotent stem cells (iPSC) (Takahashi and Yamanaka., 2006), which can be routinely established and maintained in the presence of LIF, can also be developed by exposure to FGF2, and possess full pluripotency as determined by chimera production (di Stefano et al., 2010). In addition, another type of self-renewing stem cells from preimplantation murine embryos can be established in response to FGF2, ActivinA, and the Gsk3ß inhibitor BIO (designated FAB-SC). FAB-SC has no naive pluripotency while they cannot form teratomas or contribute chimera after blastocyst injection, whereas they recovered naive pluripotency when they cultured in LIF-containing medium (Chou et al., 2008). These previous reports suggest that pluripotent stem cells exhibit plasticity in their cytokine dependence, especially during the time of their derivation.