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Cystic fibrosis (CF) is a lethal autosomal recessive disorder that afflicts more than 70,000 people. People with CF experience multi-organ dysfunction resulting from aberrant electrolyte transport across polarized epithelia due to mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. CF-related lung disease is by far the most important determinant of morbidity and mortality. Here we report results from a multi-institute consortium in which single-cell transcriptomics were applied to define disease-related changes by comparing the proximal airway of CF donors (n = 19) undergoing transplantation for end-stage lung disease with that of previously healthy lung donors (n = 19). Disease-dependent differences observed include an overabundance of epithelial cells transitioning to specialized ciliated and secretory cell subsets coupled with an unexpected decrease in cycling basal cells. Our study yields a molecular atlas of the proximal airway epithelium that will provide insights for the development of new targeted therapies for CF airway disease. Single-cell RNA profiling of human cystic fibrosis proximal airway tissue reveals an overabundance of epithelial cells transitioning to specialized ciliated and secretory cells coupled with a decrease in cycling basal cells.

Summary CpG islands often exhibit low DNA methylation, high histone H3 lysine 4 trimethylation, low nucleosome density, and high DNase I hypersensitivity, yet the rules by which CpG islands are sensed remain poorly understood. In this study, we first evaluated the relationships between the DNA and the chromatin properties of CpG islands in embryonic stem cells using modified bacterial artificial chromosomes. Then, using a bioinformatic approach, we identified strict CpG-island density and length thresholds in mouse embryonic stem and differentiated cells that consistently specify low DNA methylation levels. Surprisingly, the human genome exhibited a dramatically different relationship between DNA properties and DNA methylation levels of CpG islands. Further analysis allowed speculation that this difference is accommodated in part by evolutionary changes in the nucleotide composition of orthologous promoters. Thus, a change in the rules by which CpG-island properties are sensed may have co-evolved with compensatory genome adaptation events during mammalian evolution., Graphical abstract, Highlights • Strict DNA property rules can predict low DNA methylation at murine CpG islands • Mice and humans differ greatly in how DNA properties influence DNA methylation • Evolutionary adaptation of CpG islands compensates for the species differences, Langerman and colleagues examined relationships between DNA and chromatin properties of CpG islands. They identified rules by which the length of a CpG-rich region and CpG density influence DNA methylation. These rules differ between humans and mice, with the differences permitted during evolution by adaptations at the DNA and chromatin levels.

Viruses hijack host cell metabolism to acquire the building blocks required for replication. Understanding how SARS-CoV-2 alters host cell metabolism may lead to potential treatments for COVID-19. Here we profile metabolic changes conferred by SARS-CoV-2 infection in kidney epithelial cells and lung air-liquid interface (ALI) cultures, and show that SARS-CoV-2 infection increases glucose carbon entry into the TCA cycle via increased pyruvate carboxylase expression. SARS-CoV-2 also reduces oxidative glutamine metabolism while maintaining reductive carboxylation. Consistent with these changes, SARS-CoV-2 infection increases the activity of mTORC1 in cell lines and lung ALI cultures. Lastly, we show evidence of mTORC1 activation in COVID-19 patient lung tissue, and that mTORC1 inhibitors reduce viral replication in kidney epithelial cells and lung ALI cultures. Our results suggest that targeting mTORC1 may be a feasible treatment strategy for COVID-19 patients, although further studies are required to determine the mechanism of inhibition and potential efficacy in patients., The pandemic of COVID-19, caused by SARS-CoV-2 infection, warrants immediate investigation for therapy options. Here the authors show, using epithelial and air-liquid interface cultures, that SARS-CoV-2 hijacks host cell metabolism to facilitate viral replication, and that inhibition of mTORC1, a master metabolic regulator, suppresses viral replication.

Summary A dramatic difference in global DNA methylation between male and female cells characterizes mouse embryonic stem cells (ESCs), unlike somatic cells. We analyzed DNA methylation changes during reprogramming of male and female somatic cells and in resulting induced pluripotent stem cells (iPSCs). At an intermediate reprogramming stage, somatic and pluripotency enhancers are targeted for partial methylation and demethylation. Demethylation within pluripotency enhancers often occurs at ESC binding sites of pluripotency transcription factors. Late in reprogramming, global hypomethylation is induced in a female-specific manner. Genome-wide hypomethylation in female cells affects many genomic landmarks, including enhancers and imprint control regions, and accompanies the reactivation of the inactive X chromosome. The loss of one of the two X chromosomes in propagating female iPSCs is associated with genome-wide methylation gain. Collectively, our findings highlight the dynamic regulation of DNA methylation at enhancers during reprogramming and reveal that X chromosome dosage dictates global DNA methylation levels in iPSCs., Graphical Abstract, Highlights • Female iPSCs are globally hypomethylated • Hypomethylation affects multiple genomic features including imprint control regions • Loss of X chromosome restores global methylation but not at imprint control regions • Methylation changes at enhancers in male and female reprogramming intermediates, Somatic cells can be reprogrammed to iPSCs, inducing reactivation of the inactive X chromosome. Using genome-scale DNA methylation analyses, Plath, Pasque, and colleagues show that iPSCs adopt sex-specific differences in global DNA methylation that correlate with the presence of two active X chromosomes. Upon culture, female iPSCs lose one of the two X chromosomes and adopt male-like DNA methylation.

The developmental trajectory of human skeletal myogenesis and the transition between progenitor and stem cell states are unclear. We employed single cell RNA-sequencing to profile human skeletal muscle tissues from embryonic, fetal and postnatal stages. In silico, we identified myogenic as well as other cell types and constructed a “roadmap” of human skeletal muscle ontogeny across development. In a similar fashion, we also profiled the heterogeneous cell cultures generated from multiple human pluripotent stem cell (hPSC) myogenic differentiation protocols, and mapped hPSC-derived myogenic progenitors to an embryonic-to-fetal transition period. We found differentially enriched biological processes and discovered co-regulated gene networks and transcription factors present at distinct myogenic stages. This work serves as a resource for advancing our knowledge of human myogenesis. It also provides a tool for a better understanding of hPSC-derived myogenic progenitors for translational applications in skeletal muscle based regenerative medicine.

We performed RNA sequencing on 40,000 cells to create a high-resolution single-cell gene expres-sion atlas of developing human cortex, providing the first single-cell characterization of previously uncharacterized cell types, including human sub-plate neurons, comparisons with bulk tissue, and systematic analyses of technical factors. These data permit deconvolution of regulatory networks connecting regulatory elements and transcriptional drivers to single-cell gene expression programs, significantly extending our understanding of human neurogenesis, cortical evolution, and the cellular basis of neuropsychiatric disease. We tie cell-cycle progression with early cell fate decisions during neurogenesis, demonstrating that differentiation occurs on a transcriptomic continuum; rather than only expressing a few transcription factors that drive cell fates, differentiating cells express broad, mixed cell-type transcriptomes before telophase. By mapping neuropsychiatric disease genes to cell types, we implicate dysregulation of specific cell types in ASD, ID, and epilepsy. We developed CoDEx, an online portal to facilitate data access and browsing.

Summary Human embryonic stem cells (hESCs) display substantial heterogeneity in gene expression, implying the existence of discrete substates within the stem cell compartment. To determine whether these substates impact fate decisions of hESCs we used a GFP reporter line to investigate the properties of fractions of putative undifferentiated cells defined by their differential expression of the endoderm transcription factor, GATA6, together with the hESC surface marker, SSEA3. By single-cell cloning, we confirmed that substates characterized by expression of GATA6 and SSEA3 include pluripotent stem cells capable of long-term self-renewal. When clonal stem cell colonies were formed from GATA6-positive and GATA6-negative cells, more of those derived from GATA6-positive cells contained spontaneously differentiated endoderm cells than similar colonies derived from the GATA6-negative cells. We characterized these discrete cellular states using single-cell transcriptomic analysis, identifying a potential role for SOX17 in the establishment of the endoderm-biased stem cell state., Graphical Abstract, Highlights • Subsets of hESCs can co-express pluripotency-associated and lineage-specific genes • hESCs co-expressing GATA6 are capable of long-term self-renewal • Single GATA6-expressing hESCs regenerate GATA6-negative cells • GATA6-expressing hESCs are biased in their propensity for differentiation, Human embryonic stem cells have the capacity to turn into any cell type within the adult. Peter Andrews and colleagues have shown that subtle differences between individual cells can functionally bias the resulting cell type that is produced. Generating and purifying these biased cells may therefore improve the derivation of medically relevant cell types.