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Microscopy and fluorescence‐activated cell sorting (FACS) are two of the most important tools for single‐cell phenotyping in basic and biomedical research. Microscopy provides high‐resolution snapshots of cell morphology and the inner workings of cells, while FACS isolates thousands of cells per second using simple parameters, such as the intensity of fluorescent protein labels. Recent technologies are now combining both methods to enable the fast isolation of cells with microscopic phenotypes of interest, thereby bridging a long‐standing gap in the life sciences. In this Commentary, we discuss the technical advancements made by image‐enabled cell sorting and highlight novel experimental strategies in functional genomics and single‐cell research. Graphical Abstract This Commentary discusses the technical advancements made by image‐enabled cell sorting and highlights novel experimental strategies in functional genomics and single‐cell research.

Exacerbated pro‐inflammatory immune response contributes to COVID‐19 pathology. However, despite the mounting evidence about SARS‐CoV‐2 infecting the human gut, little is known about the antiviral programs triggered in this organ. To address this gap, we performed single‐cell transcriptomics of SARS‐CoV‐2‐infected intestinal organoids. We identified a subpopulation of enterocytes as the prime target of SARS‐CoV‐2 and, interestingly, found the lack of positive correlation between susceptibility to infection and the expression of ACE2 . Infected cells activated strong pro‐inflammatory programs and produced interferon, while expression of interferon‐stimulated genes was limited to bystander cells due to SARS‐CoV‐2 suppressing the autocrine action of interferon. These findings reveal that SARS‐CoV‐2 curtails the immune response and highlights the gut as a pro‐inflammatory reservoir that should be considered to fully understand SARS‐CoV‐2 pathogenesis. Synopsis Single cell sequencing and multiplex single‐molecule RNA FISH analyses on SARS‐CoV‐2 infected human intestinal organoids characterize the tropism of SARS‐CoV‐2 and identify strategies developed by the virus to interfere with the host intrinsic innate immune response. SARS‐CoV‐2 primarily infects the enterocyte lineage. High expression levels of ACE2 does not correlate with higher infectability of cells by SARS‐CoV‐2. ACE2 expression is downregulated upon SARS‐CoV‐2 infection of human intestinal epithelial cells. Infected cells show a high pro‐inflammatory response and little to no interferon‐mediated response as the result of a SARS‐CoV‐2‐mediated inhibition of interferon signaling. Graphical Abstract Single cell sequencing and multiplex single‐molecule RNA FISH analyses on SARS‐CoV‐2 infected human intestinal organoids characterize the tropism of SARS‐CoV‐2 and identify strategies developed by the virus to interfere with the host intrinsic innate immune response.

Severe forms of dilated cardiomyopathy (DCM) are associated with point mutations in the alternative splicing regulator RBM20 that are frequently located in the arginine/serine-rich domain (RS-domain). Such mutations can cause defective splicing and cytoplasmic mislocalization, which leads to the formation of detrimental cytoplasmic granules. Successful development of personalized therapies requires identifying the direct mechanisms of pathogenic RBM20 variants. Here, we decipher the molecular mechanism of RBM20 mislocalization and its specific role in DCM pathogenesis. We demonstrate that mislocalized RBM20 RS-domain variants retain their splice regulatory activity, which reveals that aberrant cellular localization is the main driver of their pathological phenotype. A genome-wide CRISPR knockout screen combined with image-enabled cell sorting identified Transportin-3 (TNPO3) as the main nuclear importer of RBM20. We show that the direct RBM20-TNPO3 interaction involves the RS-domain, and is disrupted by pathogenic variants. Relocalization of pathogenic RBM20 variants to the nucleus restores alternative splicing and dissolves cytoplasmic granules in cell culture and animal models. These findings provide proof-of-principle for developing therapeutic strategies to restore RBM20’s nuclear localization in RBM20-DCM patients. The authors show that loss-of-interaction with the nuclear importer, TNPO3, causes cytoplasmic mislocalization of RBM20 variants linked to severe cases of dilated cardiomyopathy. Restoring their nuclear localization alleviates the disease phenotype.

Cerebral malaria is a severe neurovascular complication of Plasmodium falciparum infection, with high mortality rates even after treatment with effective antimalarials. Limitations in current experimental models have hindered our knowledge of the disease. We developed a 3D blood-brain barrier (BBB) model with enhanced barrier properties using primary brain endothelial cells, astrocytes, and pericytes. Exposure to parasite egress products increases microvascular permeability, likely due to transcriptional downregulation of junctional and vascular development genes in endothelial cells. In addition, it increases the expression of ferroptosis markers, antigen presentation and type I interferon genes and upregulates the JAK-STAT pathway across all BBB cell types. Incubation with cytoadherent schizont-stage P. falciparum -infected erythrocytes induces a similar, but highly localized transcriptional shift, along with inter-endothelial gaps at sites of parasite egress, leading to enhanced permeability. Treatment with the JAK-STAT inhibitor Ruxolitinib prevents the increase in permeability induced by P. falciparum egress products. These findings provide key insights into the parasite-mediated mechanisms driving brain microvascular pathogenesis in cerebral malaria and suggest potential avenues for adjunctive therapies. Here the authors show that Plasmodium falciparum egress products disrupt endothelial barrier and activate JAK-STAT and interferon type response in a 3D blood-brain barrier model. Vascular disruption is reversed by Ruxolitinib, a JAK-STAT inhibitor.

During microRNA (miRNA)-guided gene silencing, Argonaute (Ago) proteins interact with a member of the TNRC6/GW protein family. Here we used a short GW protein-derived peptide fused to GST and demonstrate that it binds to Ago proteins with high affinity. This allows for the simultaneous isolation of all Ago protein complexes expressed in diverse species to identify associated proteins, small RNAs, or target mRNAs. We refer to our method as “Ago protein Affinity Purification by Peptides” (Ago-APP). Furthermore, expression of this peptide competes for endogenous TNRC6 proteins, leading to global inhibition of miRNA function in mammalian cells.

Cancer stem cells or cancer initiating cells are believed to contribute to cancer recurrence after therapy. MicroRNAs (miRNAs) are short RNA molecules with fundamental roles in gene regulation. The role of miRNAs in cancer stem cells is only poorly understood. Here, we report miRNA expression profiles of glioblastoma stem cell‐containing CD133 + cell populations. We find that miR‐9, miR‐9 * (referred to as miR‐9/9 * ), miR‐17 and miR‐106b are highly abundant in CD133 + cells. Furthermore, inhibition of miR‐9/9 * or miR‐17 leads to reduced neurosphere formation and stimulates cell differentiation. Calmodulin‐binding transcription activator 1 (CAMTA1) is a putative transcription factor, which induces the expression of the anti‐proliferative cardiac hormone natriuretic peptide A (NPPA). We identify CAMTA1 as an miR‐9/9 * and miR‐17 target. CAMTA1 expression leads to reduced neurosphere formation and tumour growth in nude mice, suggesting that CAMTA1 can function as tumour suppressor. Consistently, CAMTA1 and NPPA expression correlate with patient survival. Our findings could provide a basis for novel strategies of glioblastoma therapy. This work identifies the calmodulin‐binding transcription activator CAMTA1 as a crucial miRNA‐9/9 * target in glioblastoma, and provides evidence that CAMTA1 is a therapeutically relevant tumour suppressor.

The transcriptome contains rich information on molecular, cellular and organismal phenotypes. However, experimental and statistical limitations constrain sensitivity and throughput of genetic screening with single-cell transcriptomics readout. To overcome these limitations, we introduce targeted Perturb-seq (TAP-seq), a sensitive, inexpensive and platform-independent method focusing single-cell RNA-seq coverage on genes of interest, thereby increasing the sensitivity and scale of genetic screens by orders of magnitude. TAP-seq permits routine analysis of thousands of CRISPR-mediated perturbations within a single experiment, detects weak effects and lowly expressed genes, and decreases sequencing requirements by up to 50-fold. We apply TAP-seq to generate perturbation-based enhancer–target gene maps for 1,778 enhancers within 2.5% of the human genome. We thereby show that enhancer–target association is jointly determined by three-dimensional contact frequency and epigenetic states, allowing accurate prediction of enhancer targets throughout the genome. In addition, we demonstrate that TAP-seq can identify cell subtypes with only 100 sequencing reads per cell. Targeted sequencing of perturbation effects offers a sensitive approach to capture genes of interest in CRISPR-mediated screens, enabling genome-scale screens at higher scale and lower cost than whole-transcriptome Perturb-seq.

Cancer stem cells or cancer initiating cells are believed to contribute to cancer recurrence after therapy. MicroRNAs (miRNAs) are short RNA molecules with fundamental roles in gene regulation. The role of miRNAs in cancer stem cells is only poorly understood. Here, we report miRNA expression profiles of glioblastoma stem cell-containing CD133 super(+) cell populations. We find that miR-9, miR-9 super(*) (referred to as miR-9/9 super(*)), miR-17 and miR-106b are highly abundant in CD133 super(+) cells. Furthermore, inhibition of miR-9/9 super(*) or miR-17 leads to reduced neurosphere formation and stimulates cell differentiation. Calmodulin-binding transcription activator 1 (CAMTA1) is a putative transcription factor, which induces the expression of the anti-proliferative cardiac hormone natriuretic peptide A (NPPA). We identify CAMTA1 as an miR-9/9 super(*) and miR-17 target. CAMTA1 expression leads to reduced neurosphere formation and tumour growth in nude mice, suggesting that CAMTA1 can function as tumour suppressor. Consistently, CAMTA1 and NPPA expression correlate with patient survival. Our findings could provide a basis for novel strategies of glioblastoma therapy.

Cerebral malaria is a severe neurovascular complication of Plasmodium falciparum infection, with high mortality rates even after treatment with effective antimalarials. Limitations in current experimental models have hindered our knowledge of the disease. We developed a 3D blood-brain barrier (BBB) model with enhanced barrier properties using primary brain endothelial cells, astrocytes and pericytes. Exposure to parasite egress products increased microvascular permeability, likely due to transcriptional downregulation of junctional and vascular development genes in endothelial cells. In addition, it increased the expression of ferroptosis markers, antigen presentation and type I interferon genes and upregulated the JAK-STAT pathway across all BBB cell types. Incubation with cytoadherent schizont-stage P. falciparum-infected erythrocytes induced a similar, but highly localized transcriptional shift, along with inter-endothelial gaps at sites of parasite egress, significantly increasing permeability. The co-administration of egress products with the JAK-STAT inhibitor Ruxolitinib prevented junctional disruption and BBB breakdown. These findings provide key insights into the parasite-mediated mechanisms driving brain microvascular pathogenesis in cerebral malaria and suggest potential avenues for adjunctive therapies.