Project description:The conversion of cell fates is controlled by hierarchical gene regulatory networks (GRNs) that induce remarkable alterations of cellular and transcriptome states. The identification of key regulators within these networks from myriad of candidate genes, however, poses a major research challenge. Here we present Convert-seq, combining single-cell RNA sequencing (scRNA-seq) and pooled (mutiplexed) ectopic gene expression with a new strategy to discriminate sequencing reads derived from exogenous and endogenous transcripts. We demonstrate Convert-seq by associating hundreds of single cells at multiple time-points during direct conversion of human fibroblasts to induced neurons (iN) with exogenous and endogenous transcriptional signatures. Convert-seq simultaneously identified GRNs that modulate the emergence of parallel developmental trajectories during iN conversion and predicted combinatorial interactions of exogenous transcription factors controlling iN subtype specification. Validation of iN subtypes generated by novel combinations of exogenous transcription factors establish Convert-seq as a broadly applicable workflow to rapidly identify key transcription factors and GRNs orchestrating the direct conversion of virtually any cell type.
Project description:Pancreatic cancer is a complex disease with a desmoplastic stroma, extreme hypoxia, and inherent resistance to therapy. Understanding the signaling and adaptive response of such an aggressive cancer is key to making advances in therapeutic efficacy and understanding disease progression. Redox factor-1 (Ref-1), a redox signaling protein, regulates the DNA binding activity of several transcription factors, including HIF-1. The conversion of HIF-1 from an oxidized to reduced state leads to enhancement of its DNA binding. In our previously published work, knockdown of Ref-1 under normoxia resulted in altered gene expression patterns on pathways including EIF2, protein kinase A, and mTOR. In this study, single cell RNA sequencing (scRNA-seq) and proteomics were used to explore the effects of Ref-1 on metabolic pathways under hypoxia.Results: We also integrated the scRNA data analysis with the proteomic analysis and found that the differentially expressed genes and pathways identified from the scRNA-seq data are highly consistent to the significant proteins observed in the proteomics data, especially for the upregulated cell cycle and transcription pathways and downregulated metabolic, apoptosis and signaling pathways under hypoxia. Conclusion: The scRNA-seq and proteomics data consistently demonstrated down-regulated central metabolism pathways in APE1/Ref-1 knockdown vs scrambled control under both normoxia and hypoxia conditions. Experimental Methods: scRNA-seq comparing pancreatic cancer cells expressing less than 20% of the Ref-1 protein was analyzed using left truncated mixture Gaussian model. Matched samples were also collected for bulk proteomic analysis of the four conditions. scRNA-seq data was validated using proteomics and qRT-PCR. Ref-1’s role in mitochondrial function was confirmed using mitochondrial function assays and qRT-PCR. Results: We also integrated the scRNA data analysis with the proteomic analysis and found that the differentially expressed genes and pathways identified from the scRNA-seq data are highly consistent to the significant proteins observed in the proteomics data, especially for the upregulated cell cycle and transcription pathways and downregulated metabolic, apoptosis and signaling pathways under hypoxia. Conclusion: The scRNA-seq and proteomics data consistently demonstrated down-regulated central metabolism pathways in APE1/Ref-1 knockdown vs scrambled control under both normoxia and hypoxia conditions.
Project description:FOXO transcription factors are central regulators of longevity from worms to humans. FOXO3 – the FOXO isoform associated with exceptional human longevity – preserves adult neural stem cell pools. Here we identify FOXO3 direct targets genome-wide in primary cultures of adult neural progenitor cells (NPCs). Interestingly, FOXO3-bound sites are enriched for motifs for bHLH transcription factors and FOXO3 shares common targets with the pro-neuronal bHLH transcription factor ASCL1/MASH1 in NPCs. Analysis of the chromatin landscape reveals that FOXO3 and ASCL1 are particularly enriched at the enhancers of genes involved in neurogenic pathways. Intriguingly, FOXO3 inhibits ASCL1-dependent neurogenesis in NPCs and direct neuronal conversion in fibroblasts. FOXO3 also restrains neurogenesis in vivo. Our study identifies a genome-wide interaction between the pro-longevity transcription factor FOXO3 and the cell fate determinant ASCL1, and raises the possibility that FOXO3’s ability to restrain ASCL1-dependent neurogenesis may help preserve the neural stem cell pool. ChIP-seq profiles of two transcription factors (FOXO3 and ASCL1) and three histone marks (H3K4me1, H3K4me3 and H3K27me3) in adult mouse neural progenitor cells.
Project description:Forced expression of pro-neural transcription factors was shown to mediate direct neuronal conversion of human fibroblasts. Since neurons are postmitotic, the conversion efficiency represents an important parameter. Here we present a minimalist approach combining two factor neuronal programming with small molecule-based inhibition of GSK3ß and SMAD signaling, which gives rise to functional neuron-like cells (iNs) of various neurotransmitter phenotypes with an overall yield of up to >200% and a final neuronal purity of up to >80%. Timcourse of reprogramming of fibroblasts towards an neuronal phenotype in two independent fibroblast lines
Project description:Recent advances in direct reprogramming using cell type-specific transcription factors provide an unprecedented opportunity for rapid generation of desired human cell types from easily accessible tissues. However, due to the diversity of conversion factors that facilitate the process, an arduous screening step is inevitable to find the appropriate combination(s). Here, we show that under chemically defined conditions minimal pluripotency factors are sufficient to directly reprogram human fibroblasts into stably self-renewing neural progenitor/stem cells (NSCs), but without passing through a pluripotent intermediate stage. These NSCs can be expanded and propagated in vitro without losing their potential to differentiate into various neuronal subtypes and glia. Our direct reprogramming strategy represents a simple and advanced paradigm of direct conversion that will provide an unlimited source of human neural cells for cell therapy, disease modeling, and drug screening. We used microarray to compare the global gene expression pattern between human fibroblasts and human neural epitheliums from human ESCs or directly from fibroblasts. We cultured cells and harvested them and then extracted total RNA for microarray.
Project description:Ectopic expression of neuronal microRNAs (miRNAs), miR-9/9* and miR-124 (miR-9/9*-124) in adult human fibroblasts has been found to evoke extensive reconfigurations of the chromatin and direct the fate conversion to neurons. We found that miR-9/9* and miR-124 led to the repression of REST, a transcriptional repressor of neuronal genes, during microRNA-mediated neuronal conversion and knockdown of REST enhanced the activation of BAF53b, a mature neuronal marker. Furthermore, time series analysis of the transcriptome of cells undergoing the miR-9/9*-124-induced conversion indicated upregulated genetic pathways that were predicted to be targeted by REST although the transcript level of REST remained unchanged (Abernathy et al., 2017). Therefore, we reasoned that knocking down REST in addition to miR-9/9*-124 at an early time point (day 7), in which REST repression is minimally evident during neuronal conversion, would speed up the adoption of neuronal identity. We performed the RNA-seq analysis to compared differentially expressed genes (DEGs) between human adult fibroblasts expressing control shRNA (shCTL) and reprogramming cells expressing shCTL or shREST at day 7. Finally, we found that the repression of REST constitutes an important component of microRNA-mediated neuronal reprogramming of human fibroblasts.