A Rare Human Syndrome Provides Genetic Evidence that WNT Signaling Is Required for Reprogramming of Fibroblasts to Induced Pluripotent Stem Cells

Jason Ross,Julia Busch,Ellen Mintz,Damian Ng,Alexandra Stanley,David Brafman,V Reid Sutton,Ignatia Van Den Veyver,Karl Willert

doi:10.1016/j.celrep.2014.10.049

Abstract

WNT signaling promotes the reprogramming of somatic cells to an induced pluripotent state. We provide genetic evidence that WNT signaling is a requisite step during the induction of pluripotency. Fibroblasts from individuals with focal dermal hypoplasia (FDH), a rare genetic syndrome caused by mutations in the essential WNT processing enzyme PORCN, fail to reprogram with standard methods. This blockade in reprogramming is overcome by ectopic WNT signaling and PORCN overexpression, thus demonstrating that WNT signaling is essential for reprogramming. The rescue of reprogramming is critically dependent on the level of WNT signaling: steady baseline activation of the WNT pathway yieldskaryotypically normal iPSCs, whereas daily stimulation with Wnt3a produces FDH-iPSCs with severely abnormal karyotypes. Therefore, although WNT signaling is required for cellular reprogramming, inappropriate activation of WNT signaling induces chromosomal instability, highlighting the precarious nature of ectopic WNT activation and its tight relationship with oncogenic transformation.

Highlights

The process of converting, or reprogramming, a mature cell type to an embryonic stem celllike state requires the establishment of a transcriptional regulatory network comprised of transcription factors including POU5F1/OCT4, SOX2 and NANOG (Boyer et al, 2005; Cole et al, 2008)
Focal dermal hypoplasia (FDH) is a rare genetic syndrome with many pleiotropic consequences caused by mutations in the X-linked gene PORCN
To develop a model for this complex disorder, we sought to develop a disease-in-a-dish by first reprogramming fibroblast cultures from Focal Dermal Hypoplasia (FDH) patients to induced pluripotent stem cells (Figure 1A)

Summary

Introduction

The process of converting, or reprogramming, a mature cell type to an embryonic stem celllike state requires the establishment of a transcriptional regulatory network comprised of transcription factors including POU5F1/OCT4, SOX2 and NANOG (Boyer et al, 2005; Cole et al, 2008). In human and mouse embryonic stem cells, these factors maintain each other’s expression, and the pluripotent state, through regulatory feedback mechanisms. Disruption of this regulatory circuit causes cells to exit the pluripotent state and differentiate. Extracellular signals, such as FGF2 in human embryonic stem cells (hESCs) and LIF in mouse embryonic stem cells, influence and regulate the pluripotent state. Establishment of the OCT4-NANOG-SOX2 transcriptional regulatory network is clearly critical for the generation of induced pluripotent stem (iPS) cells, the role of extracellular signals, such as WNTs, in this process has not been examined extensively

Results

Discussion

Conclusion