An alternative pluripotent state confers interspecies chimaeric competency.

Pluripotency, the ability to generate any cell type of the body, is an evanescent attribute of embryonic cells. Transitory pluripotent cells can be captured at different time points during embryogenesis and maintained as embryonic stem cells or epiblast stem cells in culture. Since ontogenesis is a dynamic process in both space and time, it seems counterintuitive that these two temporal states represent the full spectrum of organismal pluripotency. Here we show that by modulating culture parameters, a stem-cell type with unique spatial characteristics and distinct molecular and functional features, designated as region-selective pluripotent stem cells (rsPSCs), can be efficiently obtained from mouse embryos and primate pluripotent stem cells, including humans. The ease of culturing and editing the genome of human rsPSCs offers advantages for regenerative medicine applications. The unique ability of human rsPSCs to generate post-implantation interspecies chimaeric embryos may facilitate our understanding of early human development and evolution.

Identification of novel long noncoding RNAs underlying vertebrate cardiovascular development.

BACKGROUND: Long noncoding RNAs (lncRNAs) have emerged as critical epigenetic regulators with important functions in development and disease. Here, we sought to identify and functionally characterize novel lncRNAs critical for vertebrate development. METHODS AND RESULTS: By relying on human pluripotent stem cell differentiation models, we investigated lncRNAs differentially regulated at key steps during human cardiovascular development with a special focus on vascular endothelial cells. RNA sequencing led to the generation of large data sets that serve as a gene expression roadmap highlighting gene expression changes during human pluripotent cell differentiation. Stage-specific analyses led to the identification of 3 previously uncharacterized lncRNAs, TERMINATOR, ALIEN, and PUNISHER, specifically expressed in undifferentiated pluripotent stem cells, cardiovascular progenitors, and differentiated endothelial cells, respectively. Functional characterization, including localization studies, dynamic expression analyses, epigenetic modification monitoring, and knockdown experiments in lower vertebrates, as well as murine embryos and human cells, confirmed a critical role for each lncRNA specific for each analyzed developmental stage. CONCLUSIONS: We have identified and functionally characterized 3 novel lncRNAs involved in vertebrate and human cardiovascular development, and we provide a comprehensive transcriptomic roadmap that sheds new light on the molecular mechanisms underlying human embryonic development, mesodermal commitment, and cardiovascular specification.

Understanding the molecular mechanisms of reprogramming.

Despite the profound and rapid advancements in reprogramming technologies since the generation of the first induced pluripotent stem cells (iPSCs) in 2006[1], the molecular basics of the process and its implications are still not fully understood. Recent work has suggested that a subset of TFs, so called "Pioneer TFs", play an important role during the stochastic phase of iPSC reprogramming [2-6]. Pioneer TFs activities differ from conventional transcription factors in their mechanism of action. They bind directly to condensed chromatin and elicit a series of chromatin remodeling events that lead to opening of the chromatin. Chromatin decondensation by pioneer factors progressively occurs during cell division and in turn exposes specific gene promoters in the DNA to which TFs can now directly bind to promoters that are readily accessible[2, 6]. Here, we will summarize recent advancements on our understanding of the molecular mechanisms underlying reprogramming to iPSC as well as the implications that pioneer Transcription Factor activities might play during different lineage conversion processes.

Establishment of human iPSC-based models for the study and targeting of glioma initiating cells.

Glioma tumour-initiating cells (GTICs) can originate upon the transformation of neural progenitor cells (NPCs). Studies on GTICs have focused on primary tumours from which GTICs could be isolated and the use of human embryonic material. Recently, the somatic genomic landscape of human gliomas has been reported. RTK (receptor tyrosine kinase) and p53 signalling were found dysregulated in ∼90% and 86% of all primary tumours analysed, respectively. Here we report on the use of human-induced pluripotent stem cells (hiPSCs) for modelling gliomagenesis. Dysregulation of RTK and p53 signalling in hiPSC-derived NPCs (iNPCs) recapitulates GTIC properties in vitro. In vivo transplantation of transformed iNPCs leads to highly aggressive tumours containing undifferentiated stem cells and their differentiated derivatives. Metabolic modulation compromises GTIC viability. Last, screening of 101 anti-cancer compounds identifies three molecules specifically targeting transformed iNPCs and primary GTICs. Together, our results highlight the potential of hiPSCs for studying human tumourigenesis.

In vivo activation of a conserved microRNA program induces mammalian heart regeneration.

Heart failure is a leading cause of mortality and morbidity in the developed world, partly because mammals lack the ability to regenerate heart tissue. Whether this is due to evolutionary loss of regenerative mechanisms present in other organisms or to an inability to activate such mechanisms is currently unclear. Here we decipher mechanisms underlying heart regeneration in adult zebrafish and show that the molecular regulators of this response are conserved in mammals. We identified miR-99/100 and Let-7a/c and their protein targets smarca5 and fntb as critical regulators of cardiomyocyte dedifferentiation and heart regeneration in zebrafish. Although human and murine adult cardiomyocytes fail to elicit an endogenous regenerative response after myocardial infarction, we show that in vivo manipulation of this molecular machinery in mice results in cardiomyocyte dedifferentiation and improved heart functionality after injury. These data provide a proof of concept for identifying and activating conserved molecular programs to regenerate the damaged heart.