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Phagocytosis is required for a broad range of physiological functions, from pathogen defense to tissue homeostasis, but the mechanisms required for phagocytosis of diverse substrates remain incompletely understood. Here, we developed a rapid magnet-based phenotypic screening strategy, and performed eight genome-wide CRISPR screens in human cells to identify genes regulating phagocytosis of distinct substrates. After validating select hits in focused miniscreens, orthogonal assays and primary human macrophages, we show that (1) the previously uncharacterized gene NHLRC2 is a central player in phagocytosis, regulating RhoA-Rac1 signaling cascades that control actin polymerization and filopodia formation, (2) very-long-chain fatty acids are essential for efficient phagocytosis of certain substrates and (3) the previously uncharacterized Alzheimer’s disease–associated gene TM2D3 can preferentially influence uptake of amyloid-β aggregates. These findings illuminate new regulators and core principles of phagocytosis, and more generally establish an efficient method for unbiased identification of cellular uptake mechanisms across diverse physiological and pathological contexts. Eight genome-wide CRISPR screens identify genes required for substrate-specific phagocytosis. The study highlights roles for NHLRC2 in filopodia formation, very-long-chain fatty acids in substrate-specific phagocytosis and TM2D3 in uptake of amyloid-β aggregates.

Phagocytosis is required for a broad range of physiological functions, from pathogen defense to tissue homeostasis, but the mechanisms required for phagocytosis of diverse substrates remain incompletely understood. Here, we developed a rapid magnet-based phenotypic screening strategy, and performed eight genome-wide CRISPR screens in human cells to identify genes regulating phagocytosis of distinct substrates. After validating select hits in focused miniscreens, orthogonal assays and primary human macrophages, we show that (1) the previously uncharacterized gene NHLRC2 is a central player in phagocytosis, regulating RhoA-Rac1 signaling cascades that control actin polymerization and filopodia formation, (2) very-long-chain fatty acids are essential for efficient phagocytosis of certain substrates and (3) the previously uncharacterized Alzheimer's disease-associated gene TM2D3 can preferentially influence uptake of amyloid-ß aggregates. These findings illuminate new regulators and core principles of phagocytosis, and more generally establish an efficient method for unbiased identification of cellular uptake mechanisms across diverse physiological and pathological contexts.

The contributions of individual genes to cell-scale morphology and cytoskeletal organization are challenging to define due to the wide intercellular variation of these complex phenotypes. We leveraged the controlled nature of image-based pooled screening to assess the impact of CRISPRi knockdown of 366 genes on cell and nuclear morphology in human U2OS osteosarcoma cells. Screen scale-up was facilitated by a new, efficient barcode readout method that successfully genotyped 85% of cells. Phenotype analysis using a deep learning algorithm, the β-variational autoencoder, produced a feature embedding space distinct from one derived from conventional morphological profiling, but detected similar gene hits while requiring minimal design decisions. We found 45 gene hits and visualized their effect by rationally constrained sampling of cells along the direction of phenotypic shift. By relating these phenotypic shifts to each other, we construct a quantitative and interpretable space of morphological variation in human cells.

The contributions of individual genes to cell-scale morphology and cytoskeletal organization are challenging to define due to the wide intercellular variation of these complex phenotypes. We leveraged the controlled nature of image-based pooled screening to assess the impact of CRISPRi knockdown of 366 genes on cell and nuclear morphology in human U2OS osteosarcoma cells. Screen scale-up was facilitated by a new, efficient barcode readout method that successfully genotyped 85% of cells. Phenotype analysis using a deep learning algorithm, the β-variational autoencoder, produced a feature embedding space distinct from one derived from conventional morphological profiling, but detected similar gene hits while requiring minimal design decisions. We found 45 gene hits and visualized their effect by rationally constrained sampling of cells along the direction of phenotypic shift. By relating these phenotypic shifts to each other, we construct a quantitative and interpretable space of morphological variation in human cells.Competing Interest StatementThe authors have declared no competing interest.

Macrophages phagocytose and thereby eliminate a wide array of extracellular threats, ranging from antibody-coated bacteria to apoptotic cells. Precision modulation of phagocytosis has emerged as a therapeutic strategy across a range of diseases, but is limited by our incomplete understanding of how macrophages recognize, engulf, and respond to different phagocytic targets. Here, we undertook a systematic investigation of the morphological, biophysical and regulatory differences between two major types of phagocytosis: an immunostimulatory form of phagocytosis triggered by antibody-coated targets and an immunosuppressive form triggered by phosphatidylserine (PS)-coated targets. We confirmed classic observations that antibody-mediated phagocytosis involves the extension of thin actin-rich protrusions around the target, but find that PS-mediated phagocytosis involves an unexpected combination of filopodial probing, piecemeal phagocytosis and a distinct ‘sinking’ mechanism of uptake. Using a genome-wide screening approach, we identified genes specifically required for each form of phagocytosis, including actin regulators, cell surface receptors and intracellular signaling molecules. Three cell surface receptors - TREM2, CD14 and integrin αMβ2 - were revealed as essential for PS-mediated uptake. Strikingly, each receptor exhibited a distinct pattern of localization at the plasma membrane and contributed uniquely to the organization of the PS-dependent phagocytic cup. Overall, this work reveals divergent genetic requirements for the morphologically and mechanically distinct forms of PS-mediated and antibody-mediated phagocytosis, thereby informing therapeutic strategies for substrate-specific phagocytosis modulation.