The LARGE Principle of Cellular Reprogramming: Lost, Acquired and Retained Gene Expression in Foreskin and Amniotic Fluid-Derived Human iPS Cells

Human amniotic fluid cells (AFCs) are routinely obtained for prenatal diagnostics procedures. Recently, it has been illustrated that these cells may also serve as a valuable model system to study developmental processes and for application in regenerative therapies. Cellular reprogramming is a means of assigning greater value to primary AFCs by inducing self-renewal and pluripotency and, thus, bypassing senescence. Here, we report the generation and characterization of human amniotic fluid-derived induced pluripotent stem cells (AFiPSCs) and demonstrate their ability to differentiate into the trophoblast lineage after stimulation with BMP2/BMP4. We further carried out comparative transcriptome analyses of primary human AFCs, AFiPSCs, fibroblast-derived iPSCs (FiPSCs) and embryonic stem cells (ESCs). This revealed that the expression of key senescence-associated genes are down-regulated upon the induction of pluripotency in primary AFCs (AFiPSCs). By defining distinct and overlapping gene expression patterns and deriving the LARGE (Lost, Acquired and Retained Gene Expression) Principle of Cellular Reprogramming, we could further highlight that AFiPSCs, FiPSCs and ESCs share a core self-renewal gene regulatory network driven by OCT4, SOX2 and NANOG. Nevertheless, these cell types are marked by distinct gene expression signatures. For example, expression of the transcription factors, SIX6, EGR2, PKNOX2, HOXD4, HOXD10, DLX5 and RAXL1, known to regulate developmental processes, are retained in AFiPSCs and FiPSCs. Surprisingly, expression of the self-renewal-associated gene PRDM14 or the developmental processes-regulating genes WNT3A and GSC are restricted to ESCs. Implications of this, with respect to the stability of the undifferentiated state and long-term differentiation potential of iPSCs, warrant further studies

Cholinergic neurones acquire adrenergic neurotransmitters when transplanted into an embryo

During development, cells become progressively restricted, until they reach their final phenotype. Differentiation was originally thought to be irreversible, but phenotypic plasticity has been observed in a variety of cell types, for example sympathetic neurones, the limb blastema and some glial cell types. A detailed description of the individual steps that lead to expression or reversal of phenotype is essential to understand the molecular events underlying cell differentiation. We examined whether ciliary neurones acquire adrenergic properties when exposed to a permissive embryonic environment. Cholinergic neurones were selectively labelled with a retrogradely transported marker and injected into chick embryos during active neural crest migration. Four to five days after injection, some of the labelled neurones were found in ‘adrenergic sites’ and had developed catecholamine histofluorescence. The cells had thus accumulated adrenergic neurotransmitters even after differentiation into Cholinergic neurones. This result shows that neurotransmitter plasticity occurs in Cholinergic neurones and suggests that the neurotransmitter phenotype can be modified by the embryonic environment