From skin to the treatment of diseases--the possibilities of iPS cell research in dermatology.

Induced pluripotent stem cells (iPSCs) can be generated from different somatic cell types through ectopic expression of a set of transcription factors. iPSCs acquire all the features of embryonic stem cells (ESCs) including pluripotency and can thus give rise to any cell type of the body. iPSCs comparable with ESCs are amenable for the correction of gene mutations by homologous recombination. Patient-derived iPSCs may thus be an ideal source for studying diseases in vitro and for treating different disorders in the clinic. In this review, we summarize recent advances and possibilities of iPSC research with focus on the field of dermatology.

An RNAi Screen Reveals an Essential Role for HIPK4 in Human Skin Epithelial Differentiation from iPSCs.

Molecular mechanisms responsible for the development of human skin epithelial cells are incompletely understood. As a consequence, the efficiency to establish a pure skin epithelial cell population from human induced pluripotent stem cells (hiPSCs) remains poor. Using an approach including RNAi and high-throughput imaging of early epithelial cells, we identified candidate kinases involved in their differentiation from hiPSCs. Among these, we found HIPK4 to be an important inhibitor of this process. Indeed, its silencing increased the amount of generated skin epithelial precursors at an early time point, increased the amount of generated keratinocytes at a later time point, and improved growth and differentiation of organotypic cultures, allowing for the formation of a denser basal layer and stratification with the expression of several keratins. Our data bring substantial input regarding regulation of human skin epithelial differentiation and for improving differentiation protocols from pluripotent stem cells.

Impact of preconditioning with retinoic acid during early development on morphological and functional characteristics of human induced pluripotent stem cell-derived neurons.

Human induced pluripotent stem cells (hiPSCs) are a suitable tool to study basic molecular and cellular mechanisms of neurodevelopment. The directed differentiation of hiPSCs via the generation of a self-renewable neuronal precursor cell line allows the standardization of defined differentiation protocols. Here, we have investigated whether preconditioning with retinoic acid during early neural induction impacts on morphological and functional characteristics of the neuronal culture after terminal differentiation. For this purpose we have analyzed neuronal and glial cell markers, neuronal outgrowth, soma size, depolarization-induced distal shifts of the axon initial segment as well as glutamate-evoked calcium influx. Retinoic acid preconditioning led to a higher yield of neurons vs. glia cells and longer axons than unconditioned controls. In contrast, glutamatergic activation and depolarization induced structural plasticity were unchanged. Our results show that the treatment of neuroectodermal cells with retinoic acid during early development, i.e. during the neurulation phase, increases the yield of neuronal phenotypes, but does not impact on the functionality of terminally differentiated neuronal cells.

NF1 loss induces senescence during human melanocyte differentiation in an iPSC-based model.

Neurofibromatosis type 1 (NF1) is a frequent genetic disease leading to the development of Schwann cell-derived neurofibromas or melanocytic lesions called café-au-lait macules (CALMs). The molecular mechanisms involved in CALMs formation remain largely unknown. In this report, we show for the first time pathophysiological mechanisms of abnormal melanocyte differentiation in a human NF1(+/-) -induced pluripotent stem cell (iPSC)-based model. We demonstrate that NF1 patient-derived fibroblasts can be successfully reprogrammed in NF1(+/-) iPSCs with active RAS signaling and that NF1 loss induces senescence during melanocyte differentiation as well as in patient's-derived CALMs, revealing a new role for NF1 in the melanocyte lineage.

Mediators of induced pluripotency and their role in cancer cells - current scientific knowledge and future perspectives.

The discovery that overexpression of the transcription factors Oct4, Sox2, Klf4 and c-Myc reprograms differentiated cells into "induced pluripotent stem cells" (iPSCs) has extended our understanding of mechanisms required to maintain stem cell pluripotency and to drive differentiation. Subsequently, additional factors have been discovered that are able to induce a pluripotent state. Recently several groups have succeeded in reprogramming cancer cells to iPSC-like induced pluripotent cancer cells by use of the method established for the generation of iPSCs. This discovery highlighted several striking similarities between pluripotent stem cells and cancer cells, in turn implying that tumorigenesis and reprogramming are partly promoted by overlapping mechanisms. Thus, research on reprogramming might help unravel the mechanisms of carcinogenesis, and vice versa. This review gives an overview of the common features of pluripotent stem cells and cancer cells and summarizes the present state of knowledge in the field of cancer cell reprogramming.