Generation of Mouse STO Feeder Cell Lines That Confer Resistance to Several Types of Selective Drugs

Purification of Mouse Embryonic Fibroblasts (MEFs)

Mouse embryonic fibroblasts (MEFs) are primary fibroblasts purified from mouse embryos at a defined time post-fertilization. MEFs have versatile applications, including use as feeder cell layers or sources of untransformed primary cells for a variety of biological assays. MEFs are most commonly isolated between embryonic day (E)12.5 and E13.5 but can be isolated from embryos as early as E8.5 and as late as E15.5. The individual embryos are harvested by carefully removing uterine tissue, yolk sac, and placenta. The embryos are euthanized, and non-mesenchymal tissues, such as the fetal liver and heart, are removed before tissue homogenization. The remaining fetal tissue is homogenized by mechanical mincing using a sterile blade, followed by enzymatic digestion and resuspension. During tissue dissociation, the duration of trypsin-EDTA/DNase digestion and enzyme concentration are critical parameters to produce high-quality MEFs with the highest rates of cell viability and proliferation potential. MEFs can be cryopreserved at passage (P) 0 if >80% confluent, passaged for further expansion before freezing down, or directly utilized for downstream applications, i.e., preparation as feeder cell layers. Primary MEFs possess a limited proliferation capacity of ∼20 cell divisions, beyond which the percentage of senescent cells rapidly increases; thus, cultures should only be expanded/passaged to a maximum of P5. Critical for cell viability during cryopreservation and thawing of MEFs is the slow decrease in temperature when freezing, the rapid increase when thawing, the use of a cryoprotective agent, and an optimal cell density. While it is critical to generate high-quality MEFs to standardize and optimize preparation procedures and utilize fresh reagents, some variability in proliferation capacity and cell viability between MEF preparations remains. Thus, MEF preparation, culture, and cryopreservation procedures are continuously being optimized. © 2023 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol: Purification, passaging, and expansion of MEFs Supporting Protocol: Cryopreservation and thawing of MEFs.

The Role of Genetically Modified Human Feeder Cells in Maintaining the Integrity of Primary Cultured Human Deciduous Dental Pulp Cells

Tissue-specific stem cells exist in tissues and organs, such as skin and bone marrow. However, their pluripotency is limited compared to embryonic stem cells. Culturing primary cells on plastic tissue culture dishes can result in the loss of multipotency, because of the inability of tissue-specific stem cells to survive in feeder-less dishes. Recent findings suggest that culturing primary cells in medium containing feeder cells, particularly genetically modified feeder cells expressing growth factors, may be beneficial for their survival and proliferation. Therefore, the aim of this study was to elucidate the role of genetically modified human feeder cells expressing growth factors in maintaining the integrity of primary cultured human deciduous dental pulp cells. Feeder cells expressing leukemia inhibitory factor, bone morphogenetic protein 4, and basic fibroblast growth factor were successfully engineered, as evidenced by PCR. Co-culturing with mitomycin-C-treated feeder cells enhanced the proliferation of newly isolated human deciduous dental pulp cells, promoted their differentiation into adipocytes and neurons, and maintained their stemness properties. Our findings suggest that genetically modified human feeder cells may be used to maintain the integrity of primary cultured human deciduous dental pulp cells.

Characterization of induced tissue-specific stem cells from pancreas by a synthetic self-replicative RNA

Induced pluripotent stem (iPS) cells have significant implications for overcoming most of the ethical issues associated with embryonic stem (ES) cells. Furthermore, our recent study demonstrated the generation of induced tissue-specific stem (iTS) cells by transient overexpression of the reprogramming factors using a plasmid combined with tissue-specific selection. In this study, we were able to generate RNA-based iTS cells that utilize a single, synthetic, self-replicating VEE-RF RNA replicon expressing four reprogramming factors (OCT4, KLF4, SOX2, and GLIS1). A single VEE-RF RNA transfection into mouse pancreatic tissue resulted in efficient generation of iTS cells from pancreas (iTS-P cells) with genetic markers of endoderm and pancreatic progenitors and differentiation into insulin-producing cells more efficiently than ES cells. Subcutaneous transplantation of iTS-P cells into immunodeficient mice resulted in no teratoma formation. Bisulfite genomic sequencing demonstrated that the promoters of Oct4 and Nanog remained partially methylated in iTS-P cells. We compared the global gene-expression profiles of ES cells, iTS-P cells, and pancreatic islets. Microarray analyses confirmed that the iTS-P cells were similar but not identical to ES cells compared with islets. These data suggest that iTS-P cells are cells that inherit numerous components of epigenetic memory from pancreas cells and acquire self-renewal potential. The generation of iTS cells may have important implications for the clinical application of stem cells.

The Development of Cancer through the Transient Overexpression of Reprogramming Factors

Although induced pluripotent stem (iPS) cells have significant implications for overcoming most of the ethical issues associated with embryonic stem cells, several issues related to the use of iPS cells in clinical applications remain unresolved, including the issue of teratoma formation. We previously reported that the induction of induced tissue-specific stem (iTS) cells from the pancreas (iTS-P) or liver (iTS-L) by the transient overexpression of reprogramming factors, combined with tissue-specific selection and the generation of iTS cells, could have important implications for the clinical application of stem cells. At the same time, we also generated "induced fibroblast-like (iF) cells" that were capable of self-renewal, which had a similar morphology to fibroblast cells. In this study, we evaluated iF cells. iF cells are unlikely to show adipogenic/osteogenic differentiation. Moreover, iF cells have the ability to form tumors and behave similarly to pancreatic cancer cells. The technology used in the generation of iPS/iTS cells is also associated with the risk of generating cancer-like cells.

Choice of Feeders Is Important When First Establishing iPSCs Derived From Primarily Cultured Human Deciduous Tooth Dental Pulp Cells

Feeder cells are generally required to maintain embryonic stem cells (ESCs)/induced pluripotent stem cells (iPSCs). Mouse embryonic fibroblasts (MEFs) isolated from fetuses and STO mouse stromal cell line are the most widely used feeder cells. The aim of this study was to determine which cells are suitable for establishing iPSCs from human deciduous tooth dental pulp cells (HDDPCs). Primary cultures of HDDPCs were cotransfected with three plasmids containing human OCT3/4, SOX2/KLF4, or LMYC/LIN28 and pmaxGFP by using a novel electroporation method, and then cultured in an ESC qualified medium for 15 days. Emerging colonies were reseeded onto mitomycin C-treated MEFs or STO cells. The colonies were serially passaged for up to 26 passages. During this period, colony morphology was assessed to determine whether cells exhibited ESC-like morphology and alkaline phosphatase activity to evaluate the state of cellular reprogramming. HDDPCs maintained on MEFs were successfully reprogrammed into iPSCs, whereas those maintained on STO cells were not. Once established, the iPSCs were maintained on STO cells without loss of pluripotency. Our results indicate that MEFs are better feeder cells than STO cells for establishing iPSCs. Feeder choice is a key factor enabling efficient generation of iPSCs.

Induction of tissue-specific stem cells by reprogramming factors, and tissue-specific selection

Although induced pluripotent stem (iPS) cells have significant implications for overcoming most of the ethical issues associated with embryonic stem (ES) cells, there are still several unresolved issues related to the use of iPS cells for clinical applications, such as teratoma formation. In this study, we were able to generate tissue-specific stem (induced tissue-specific stem; iTS) cells from the pancreas (iTS-P) or liver (iTS-L) by transient overexpression of reprogramming factors, combined with tissue-specific selection. The generation of iTS cells was easier than that of iPS cells. The iTS-P/iTS-L cells express genetic markers of endoderm and pancreatic/hepatic progenitors and were able to differentiate into insulin-producing cells/hepatocytes more efficiently than ES cells. Subcutaneous transplantation of both types of iTS cells into immunodeficient mice resulted in no teratoma formation. The technology used for the transient overexpression of reprogramming factors and tissue-specific selection may be useful for the generation of other tissue-specific stem cells, and the generation of iTS cells could have important implications for the clinical application of stem cells.