Low-molecular-weight inhibitors of cell differentiation enable efficient growth of mouse iPS cells under feeder-free conditions

Generation of mouse iPS cells using an inducible expression of transgenes via the cumate gene-switch

We applied an inducible gene expression system that utilizes the p-cmt operon, the cumate gene-switch, to generate mouse induced pluripotent stem (iPS) cells. Mouse embryonic fibroblast (MEF) E6E7-MEF cells were transfected with a single cumate gene-switch vector enabling concomitant expression of Oct4, Sox2, c-Myc, Klf4, and Gfp. Then, the cells were cultured with cumate, a monoterpene. An increase in colonies positive for alkaline phosphatase activity was observed dose-dependently with cumate. In the absence of cumate, the expression of GFP, a marker for transgene expression, was undetectable in tightly aggregated iPS cell-like colonies with endogenous expression of NANOG and OCT4. From primary MEFs using the cumate gene-switch, we also isolated iPS cells expressing endogenous NANOG, OCT4, SOX2, KLF4, and SSEA1 with hypo-methylated genomic promoter regions of endogenous Nanog and Oct4. In embryoid bodies with the progression of differentiation, expression of markers for all three germ layers was detected, and contracting cardiomyocytes were observed. Overall, we suggest that the cumate gene-switch is applicable for the generation of mouse iPS cells. The cumate gene-switch in combination with other inducible systems, such as the tet system, may provide useful approaches for analyzing the roles of transgenes underlying the establishment of iPS cells.

Optimized conditions for the supplementation of human-induced pluripotent stem cell cultures with a GSK-3 inhibitor during embryoid body formation with the aim of inducing differentiation into mesodermal and cardiac lineage

We optimized the conditions for the differentiation of human induced pluripotent stem cells (hiPSCs) into mesoderm lineage-committed cells by supplementing the cultures with CHIR, a selective GSK-3 inhibitor, during embryoid body (EB) formation. In vitro treatment with 4 μM CHIR during the late 2 days of a 4-day suspension culture period was most effective at promoting mesodermal differentiation. The resulting EBs showed a significant increase in the expression levels of mesoderm-associated genes (WNT3A, T, DKK1, GATA4, FOXC1, and MESP1) and a maintenance of OCT3/4 and NANOG expressions. Upon subsequent differentiation into a cardiac cell lineage, these EBs were shown to generate contractile cardiomyocytes. When shortening the CHIR treatment period to 1 day, the resulting EBs showed reduced expression of mesoderm-associated genes in comparison to the 2-day CHIR treatment. In particular, the expression level of FOXC1 in the 1-day CHIR-treated EBs was much lower than that of the 2-day CHIR-treated EBs. When the treatment period with CHIR was extended to 4 days, the resulting EBs presented significantly reduced expression of WNT3A, OCT3/4, and NANOG upon CHIR concentrations above 4 μM. Similarly, when CHIR treatment was conducted after the formation of EBs, the effectiveness of the GSK-3 inhibitor was reduced compared to a treatment performed during EB formation. Our results indicate that spatiotemporal constraints associated with EB formation, i.e., three-dimensional structuration and cell development in EBs, should be taken into account when designing EB formation-based differentiation protocol involving CHIR treatment.

Interaction of fibroblasts and induced pluripotent stem cells with poly(vinyl alcohol)-based hydrogel substrates

Induced pluripotent stem cells (iPSCs) provide a promising means of creating custom-tailored cell lines for cellular therapies. Their application in regenerative medicine, however, depends on the possibility that the maintenance and differentiation of cells and organs occur under defined conditions. One major component of stem cell culture systems is the substrate, where the cells must attach and proliferate. The present study aimed to investigate the putative cytotoxic effects of poly(vinyl alcohol) (PVA)-based matrices on the in vitro culture of mouse fetal fibroblasts. In addition, the PVA-based hydrogels were used to determine the capacity of bovine induced pluripotent stem cells (biPSCs) to adhere and proliferate on synthetic substrates. Our results show that both cell types interacted with the substrate and presented proliferation during culture. The biPSCs formed new colonies when cell suspensions were placed onto the hydrogel surface for culture. These results may represent a new characterized xeno-free clinical grade culture system to be widely applied in cell-based therapies.

The poly-cistronic expression of four transcriptional factors (CRX, RAX, NEURO-D, OTX2) in fibroblasts via retro- or lentivirus causes partial reprogramming into photoreceptor cells

The introduction of four key transcriptional factors (CRX, RAX, NEURO-D, OTX2) allows the direct differentiation of fibroblasts to retinal photoreceptor cells. This reprogramming was achieved with a combination of mono-cistronic viruses. Although the combination of mono-cistronic viruses was useful, a relatively high titer of recombinant viruses was necessary because co-infections are required. To overcome this issue, we established a poly-cistronic expression system for direct reprogramming and analyzed the biological characteristics of introduced cells after the exogenous introduction. The coding region of four reprogramming factors and EGFP (CRX, RAX, NEURO-D, OTX2, and EGFP; CNROE) was inserted into multiple sites of the pMYs-IP retrovirus or CSII-CMV lentivirus vector. The recombinant viruses were exposed to HE16 human embryonic fibroblasts. The expression levels of cone related genes were detected with real-time PCR. We detected the activation of two of the photoreceptor-related genes after the poly-cistronic expression of CRX, RAX, NEURO-D, and OTX2, but the rest of the genes did not exhibit transcriptional elevation. We concluded that the poly-cistronic expression of CNROE induced partial reprogramming into photoreceptor cells. We hypothesize that the direct reprogramming into photoreceptor cells might require relatively high protein expression levels of transcriptional factors.