As an alternative to working with embryonic stem cells, some scientists are researching better ways to generate iPS cells: induced pluripotent stem cells. In the embryonic state, cells havenít yet differentiated, but as adults, we have all kinds of different types of cells in our bodies: muscle, skin, liver, kidney etc. The sizes and shapes of these cells vary, in addition to some of the biomolecules they produce, as they carry out their specific functions. In order to revert cells from this specialized state back to pluripotency, the chain of biochemical commands that cause differential gene expression, needs to be turned off or blocked. This is often done using viral vectors that express certain transcription factors (TFs) that control gene methylation.
Some of the TFs that have been studied and used to make iPS cells are: c-Myc, Oct4, Oct3, Sox2, Klf4, Nanog, and Lin28. c-Myc regulates cell proliferation, growth and death. Nanog, Sox2 and Oct3/4 are believed to work together to control expression of other TFs. Lin28 blocks siRNA transcript processing. Klf4 is a tumor suppressor gene, which controls transcription of p53, a known oncogene (a gene with strong links to tumor induction).
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Viswanathan, S. et al. 2008. Selective blockade of microRNA processing by Lin28. Science 320(5872):97-100. doi:10.1126/science.1154040.
Rowland, B. et al., 2005. The KLF4 tumour suppressor is a transcriptional repressor of p53 that acts as a context-dependent oncogene. Nature Cell Biology 7:1074-1082. doi:10.1038/ncb1314.