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Brain organoids have been proposed as suitable human brain model candidates for a variety of applications. However, the lack of appropriate maturation limits the transferability of such functional tools. Here, we present a method to facilitate neuronal maturation by integrating astrocyte-secreted factors into hPSC-derived 2D and 3D neural culture systems. We demonstrate that protein- and nutrient-enriched astrocyte-conditioned medium (ACM) accelerates neuronal differentiation with enlarged neuronal layer and the overproduction of deep-layer cortical neurons. We captured the elevated changes in the functional activity of neuronal networks within ACM-treated organoids using comprehensive electrophysiological recordings. Furthermore, astrocyte-secreted cues can induce lipid droplet accumulation in neural cultures, offering protective effects in neural differentiation to withstand cellular stress. Together, these data indicate the potential of astrocyte secretions to promote neural maturation. Subject terms: Neurological models, Neuronal development

Single-cell RNA sequencing (scRNA-seq) facilitates the study of transcriptome diversity in individual cells. Yet, many existing methods lack sensitivity and accuracy. Here we introduce SCALPEL, a Nextflow-based tool to quantify and characterize transcript isoforms from standard 3’ scRNA-seq data. Using synthetic data, SCALPEL demonstrates higher sensitivity and specificity compared to other tools. In real datasets, SCALPEL predictions have a high agreement with other tools and can be experimentally validated. The use of SCALPEL on real datasets reveals novel cell populations undetectable using single-cell gene expression data, confirms known 3’ UTR length changes during cell differentiation, and identifies cell-type specific miRNA signatures regulating isoform expression. Additionally, we show that SCALPEL improves isoform quantification using paired long- and short-read scRNA-seq data. Overall, SCALPEL expands the current scRNA-seq toolkit to explore post-transcriptional gene regulation across species, tissues, and technologies, advancing our understanding of gene regulatory mechanisms at the single-cell level. Single-cell RNA-seq facilitates the study of transcriptome diversity in individual cells. Here, authors introduce a tool for isoform quantification at the single-cell level using 3’ scRNA-seq data, contributing to the study of post-transcriptional gene regulation in individual cells.

ABSTRACTProneural genes are conserved drivers of neurogenesis across the animal kingdom. How their functions have adapted to guide human-specific neurodevelopmental features is poorly understood. Here, we mined transcriptomic data from human fetal cortices and generated from human embryonic stem cell-derived cortical organoids (COs) to show that NEUROG1 and NEUROG2 are most highly expressed in basal neural progenitor cells, with pseudotime trajectory analyses indicating that NEUROG1-derived lineages predominate early and NEUROG2 lineages later. Using ChIP-qPCR, gene silencing and overexpression studies in COs, we show that NEUROG2 is necessary and sufficient to directly transactivate known target genes (NEUROD1, EOMES, RND2). To identify new targets, we engineered NEUROG2-mCherry knock-in human embryonic stem cells for CO generation. The mCherry-high CO cell transcriptome is enriched in extracellular matrix-associated genes, and two genes associated with human-accelerated regions: PPP1R17 and FZD8. We show that NEUROG2 binds COL1A1, COL3A1 and PPP1R17 regulatory elements, and induces their ectopic expression in COs, although NEUROG2 is not required for this expression. Neurog2 similarly induces Col3a1 and Ppp1r17 in murine P19 cells. These data are consistent with a conservation of NEUROG2 function across mammalian species. Summary: Analysis of human cortical organoids reveals that NEUROG1 lineages prevail early and NEUROG2 lineages later, and that NEUROG2 targets include COL genes and PPP1R17, a human-accelerated region-associated gene.