Abstract
Conventional human induced pluripotent stem cells (hiPSCs), reprogrammed from somatic cells by induced expression of Oct4, Sox2, Klf4, and c-Myc, are phenotypically different from mouse embryonic stem cells (ESCs). In mice, culture in N2B27 serum-free 2i media (mitogen-activated protein kinase/extracellular signal-regulated kinase and glycogen synthase kinase 3 inhibitors; PD0325901 and CHIR99021) plus leukemia inhibitory factor (LIF) (2i+LIF medium) enriches for germline competent ESCs. Here, we demonstrate that flat-shaped hiPSC colonies can be reprogrammed into bowl-shaped multi-potent stem cells (2i-hiPSCs) by using 2i+LIF medium. Mechanical dissociation of 2i-hiPSC colonies enables stable maintenance for >20 passages. Importantly, gene expression profiling demonstrated that 2i-hiPSCs more closely resemble primitive neural stem cells (PNSCs). Notably, this 2i-induced phenotype was generated from conventional hiPSCs, but not human ESCs (hESCs), thus correlating with the observation of neuroectodermal SOX1-positive colonies in conventional hiPSCs, but not hESCs in 2i+LIF medium. Thus, 2i-hiPSCs, which are nonteratoma forming PNSCs, may represent a safe source of cells for neural research and regenerative medicine.
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