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Summary: Norrin (NDP) and WNT7A/B induce and maintain the blood-brain and blood-retina barrier (BBB, BRB) by stimulating the Frizzled4-LDL receptor related protein 5/6 (FZD4-LRP5/6) complex to induce beta-catenin-dependent signaling in endothelial cells (ECs). Recently developed agonists for the FZD4-LRP5 complex have therapeutic potential in retinal and neurological diseases. Here, we use the tetravalent antibody modality F4L5.13 to identify agonist activities in Tspan12−/− mice, which display a complex retinal pathology due to impaired NDP-signaling. F4L5.13 administration during development alleviates BRB defects, retinal hypovascularization, and restores neural function. In mature Tspan12−/− mice F4L5.13 partially induces a BRB de novo without inducing angiogenesis. In a genetic model of impaired BRB maintenance, administration of F4L5.13 rapidly and substantially restores the BRB. scRNA-seq reveals perturbations of key mediators of barrier functions in juvenile Tspan12−/− mice, which are in large parts restored after F4L5.13 administration. This study identifies transcriptional and functional activities of FZD4-LRP5 agonists.

Summary: G3BP RNA-binding proteins are important components of stress granules (SGs). Here, we analyze the role of the Drosophila G3BP Rasputin (RIN) in unstressed cells, where RIN is not SG associated. Immunoprecipitation followed by microarray analysis identifies over 550 mRNAs that copurify with RIN. The mRNAs found in SGs are long and translationally silent. In contrast, we find that RIN-bound mRNAs, which encode core components of the transcription, splicing, and translation machinery, are short, stable, and highly translated. We show that RIN is associated with polysomes and provide evidence for a direct role for RIN and its human homologs in stabilizing and upregulating the translation of their target mRNAs. We propose that when cells are stressed, the resulting incorporation of RIN/G3BPs into SGs sequesters them away from their short target mRNAs. This would downregulate the expression of these transcripts, even though they are not incorporated into stress granules. : Laver et al. show that in early embryos, Rasputin, the Drosophila G3BP ortholog, binds short mRNAs and is associated with polysomes. They provide evidence for a direct role for Rasputin and its human homologs in stabilizing and upregulating the translation of their target mRNAs. Keywords: RNA-binding protein, post-transcriptional regulation, mRNA translation, mRNA stability, stress granule, Drosophila, embryo, G3BP, Rasputin

Summary: Glioblastoma therapies have remained elusive due to limitations in understanding mechanisms of growth and survival of the tumorigenic population. Using CRISPR-Cas9 approaches in patient-derived GBM stem cells (GSCs) to interrogate function of the coding genome, we identify actionable pathways responsible for growth, which reveal the gene-essential circuitry of GBM stemness and proliferation. In particular, we characterize members of the SOX transcription factor family, SOCS3, USP8, and DOT1L, and protein ufmylation as important for GSC growth. Additionally, we reveal mechanisms of temozolomide resistance that could lead to combination strategies. By reaching beyond static genome analysis of bulk tumors, with a genome-wide functional approach, we reveal genetic dependencies within a broad range of biological processes to provide increased understanding of GBM growth and treatment resistance. : MacLeod et al. describe genome-wide CRISPR-Cas9 screens identifying genetic vulnerabilities across a panel of patient-derived glioblastoma stem cell cultures. Regulators of stemness (SOX2, SOX9, DOT1L, and SOCS3) and stress response (ufmylation and ERAD pathways) govern the growth of glioblastoma stem cells. Chemogenomic screens using temozolomide identify modulators of sensitivity to chemotherapy. Keywords: glioblastoma, glioblastoma stem cells, CRISPR-Cas9, fitness genes, functional genomics