Project description:Human neurons engineered from induced pluripotent stem cells (iPSCs) through Neurogenin 2 (Ngn2) overexpression are widely used to study neuronal differentiation mechanisms and to model neurological diseases. However, the differentiation paths and heterogeneity of emerged neurons have not been fully explored. Here we used single-cell transcriptomics to dissect the cell states that emerge during Ngn2 overexpression across a time course from pluripotency to neuron functional maturation. We find a substantial molecular heterogeneity in the neuron types generated, with at least two populations that express genes associated with neurons of the peripheral nervous system. Neuron heterogeneity is observed across multiple iPSC clones and lines from different individuals. We find that neuron fate acquisition is sensitive to Ngn2 expression level and the duration of Ngn2 forced expression. Our data reveals that Ngn2 dosage can regulate neuron fate acquisition, and that Ngn2-iN heterogeneity can confound results that are sensitive to neuron type.
Project description:Polycomb repressive complex 2 and the epigenetic mark that it deposits, H3K27me3, are evolutionarily conserved and play critical roles in development and cancer. However, their roles in cell fate decisions in early embryonic development remain poorly understood. Here we report that knockout of polycomb repressive complex 2 genes in human embryonic stem cells causes pluripotency loss and spontaneous differentiation toward a meso-endoderm fate, owing to de-repression of BMP signalling. Moreover, human embryonic stem cells with deletion of EZH1 or EZH2 fail to differentiate into ectoderm lineages. We further show that polycomb repressive complex 2-deficient mouse embryonic stem cells also release Bmp4 but retain their pluripotency. However, when converted into a primed state, they undergo spontaneous differentiation similar to that of hESCs. In contrast, polycomb repressive complex 2 is dispensable for pluripotency when human embryonic stem cells are converted into the naive state. Our studies reveal both lineage- and pluripotent state-specific roles of polycomb repressive complex 2 in cell fate decisions.
Project description:Cancer stem cells (CSCs) are resistant to conventional chemotherapy and are hence responsible for cancer relapse. Pluripotency is a characteristic of CSCs which allows them to rapidly proliferate while maintaining the ability to differentiate into various lineages. We found that TAp73, but not its homologue p53, is required for the pluripotency of CSCs. TAp73 knockdown (KD) decreased SOD1 levels, increased ROS production and disturbed metabolism which induced differentiation and abrogated pluripotency in CSCs. TAp73 related decrease in pluripotency is linked to increased autophagy and senescence in CSCs. Furthermore, TAp73 KD also decreased the levels of pluripotency factor Sox-2 within heterogeneous cancer cell lines. Interestingly, TAp73-deficient CSCs strongly lose tumorigenic potential in mice and tumors that did form had significantly lower levels of SOD1 and pluripotency marker Oct4. Our findings reveal a unique role of TAp73 in CSCs development that is important to consider while devising future therapeutic strategies against cancer.
Project description:Stem cell engineering and grafting of mesencephalic dopamine (mesDA) neurons provides a promising strategy for brain repair in Parkinson’s disease (PD). However, essential refinement of differentiation protocols will require deeper interrogation of mesDA neuron lineage development. Here we studied neuronal development at the transcriptome-wide expression level by single-cell RNA sequencing of cells expressing the mesDA neuron transcription factor determinant Lmx1a. This approach resolved the differentiation of mesDA and neighboring neuronal lineages and revealed a remarkably close relationship between developing mesDA and subthalamic nucleus (STN) neurons. The combined ablation of Lmx1a and Lmx1b in mice disrupted both STN and mesDA neural development, while a distinct transcription factor set defined progenitors developing into STN neurons. Importantly, markers previously used to guide stem cell engineering into human mesDA neurons are shared between the two lineages. These results have important implications for stem cell engineering into mesDA neurons for cell replacement therapy in PD.
Project description:The transcriptional programs that establish neuronal identity evolved to produce a rich diversity of neuronal cell types that arise sequentially during development. Remarkably, transient expression of certain transcription factors (TFs) can also endow non-neural cells with neuronal properties. To decipher the relationship between reprogramming factors and transcriptional networks that produce neuronal identity and diversity, we screened ~600 TF pairs and identified 76 that produce induced neurons (iNs) from fibroblasts. By intersecting the transcriptomes of iNs with those of endogenous neurons, we define a “core” cell-autonomous neuronal signature. The iNs also exhibit diversity; each TF pair produces iNs with unique transcriptional patterns that can predict their pharmacological responses. By linking distinct TF input “codes” to defined transcriptional outputs, this study uncovers cell autonomous features of neuronal identity and expands the reprogramming toolbox to enable more facile engineering of induced neurons with desired patterns of gene expression and related functional properties.