Epigenetic gene silencing is seen in several repeat-expansion diseases. In fragile X syndrome, the most common genetic form of mental retardation, a CGG trinucleotide–repeat expansion adjacent to the fragile X mental retardation 1 (FMR1) gene promoter results in its epigenetic silencing. Here, we show that FMR1 silencing is mediated by the FMR1 mRNA. The FMR1 mRNA contains the transcribed CGG-repeat tract as part of the 5′ untranslated region, which hybridizes to the complementary CGG-repeat portion of the FMR1 gene to form an RNA·DNA duplex. Disrupting the interaction of the mRNA with the CGG-repeat portion of the FMR1 gene prevents promoter silencing. Thus, our data link trinucleotide-repeat expansion to a form of RNA-directed gene silencing mediated by direct interactions of the trinucleotide-repeat RNA and DNA.

Previous efforts to differentiate human embryonic stem cells (hESCs) into endothelial cells have not achieved sustained expansion and stability of vascular cells. To define vasculogenic developmental pathways and enhance differentiation, we used an endothelial cell-specific VE-cadherin promoter driving green fluorescent protein (GFP) (hVPr-GFP) to screen for factors that promote vascular commitment. In phase 1 of our method, inhibition of transforming growth factor (TGF)β at day 7 of differentiation increases hVPr-GFP + cells by tenfold. In phase 2, TGFβ inhibition maintains the proliferation and vascular identity of purified endothelial cells, resulting in a net 36-fold expansion of endothelial cells in homogenous monolayers, which exhibited a transcriptional profile of Id1 high VEGFR2 high VE-cadherin + ephrinB2 + . Using an Id1-YFP hESC reporter line, we showed that TGFβ inhibition sustains Id1 expression in hESC-derived endothelial cells and that Id1 is required for increased proliferation and preservation of endothelial cell commitment. Our approach provides © 2010 Nature America, Inc. All rights reserved.Correspondence should be addressed to S.R. (srafii@med.cornell.edu).. 7 Present address: Weill Cornell Medical College, New York, New York, USA. 8 These authors contributed equally to this work. AUTHOR CONTRIBUTIONS D.J. designed and performed the experiments and wrote the manuscript. H.-s.N. and R.B. designed and created the Id1-YFP BAC transgenic vector. M.S. performed experiments and contributed to the manuscript. D.N. performed flow cytometric experiments. T.J. performed molecular cloning. M.T. and L.S. generated the Id1-YFP BAC transgenic hESC line. L.S. and G.L. generated the FD iPSC line. N.Z. and Z.R. generated the hESC lines WMC2, WMC8 and WMC9. D.L. and S.Y.R. designed experiments and performed data analysis. S.R. designed experiments and wrote the manuscript. Accession codes. GEO: GSE19735.Note: Supplementary information is available on the Nature Biotechnology website. COMPETING INTERESTS STATEMENTThe authors declare no competing financial interests. Human embryonic stem cells (hESCs), which self-renew indefinitely 1 , offer a plentiful source of endothelial cells for therapeutic revascularization. However, few studies have identified specific developmental stimuli sufficient to support the specification and maintenance of large numbers of functional and vascular-committed endothelial cells from hESCs [2][3][4][5][6][7] . Although small numbers of hESC-derived endothelial cells have been generated in short-term cultures, these cells have not been subjected to sustained expansion, angiogenic profiling or interrogated as to the stability of vascular fate. As a result, molecular pathways that maintain vascular identity and long-term expansion of hESC-derived endothelial cells remain unknown. NIH Public AccessTo detect the emergence of endothelial cells from differentiating hESCs in real time, we generated a cell line for endothelial cell-specific lineage tracing. We cloned a 1.5-kilobase f...

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Visual morphology assessment is routinely used for evaluating of embryo quality and selecting human blastocysts for transfer after in vitro fertilization (IVF). However, the assessment produces different results between embryologists and as a result, the success rate of IVF remains low. To overcome uncertainties in embryo quality, multiple embryos are often implanted resulting in undesired multiple pregnancies and complications. Unlike in other imaging fields, human embryology and IVF have not yet leveraged artificial intelligence (AI) for unbiased, automated embryo assessment. We postulated that an AI approach trained on thousands of embryos can reliably predict embryo quality without human intervention. We implemented an AI approach based on deep neural networks (DNNs) to select highest quality embryos using a large collection of human embryo time-lapse images (about 50,000 images) from a high-volume fertility center in the United States. We developed a framework (STORK) based on Google’s Inception model. STORK predicts blastocyst quality with an AUC of >0.98 and generalizes well to images from other clinics outside the US and outperforms individual embryologists. Using clinical data for 2182 embryos, we created a decision tree to integrate embryo quality and patient age to identify scenarios associated with pregnancy likelihood. Our analysis shows that the chance of pregnancy based on individual embryos varies from 13.8% (age ≥41 and poor-quality) to 66.3% (age <37 and good-quality) depending on automated blastocyst quality assessment and patient age. In conclusion, our AI-driven approach provides a reproducible way to assess embryo quality and uncovers new, potentially personalized strategies to select embryos.