A method of screening for genetic modifiers of tau aggregation, comprising: (a) providing a population of cells comprising a Cas protein, a first tau repeat domain linked to a first reporter, and a second tau repeat domain linked to a second reporter, wherein the cells are mammalian cells, wherein the first reporter and the second reporter are fluorescent proteins, and wherein the first reporter and the second reporter are a fluorescence resonance energy transfer (FRET) pair; (b) introducing into the population of cells a library comprising a plurality of unique guide RNAs that target a plurality of genes; (c) culturing the population of cells to allow genome editing and expansion, wherein the plurality of unique guide RNAs form complexes with the Cas protein, and the Cas protein cleaves the plurality of genes resulting in knockout of gene function to produce a genetically modified population of cells; (d) contacting the genetically modified population of cells with a tau seeding agent to produce a seeded population of cells, wherein step (d) comprises culturing the genetically modified population of cells in the presence of conditioned medium harvested from cultured tau-aggregation-positive cells in which a tau repeat domain stably presents in an aggregated state, wherein the conditioned medium was harvested after being on confluent tau-aggregation-positive cells for 1 to 7 days; (e) culturing the seeded population of cells to allow tau aggregates to form, wherein aggregates of the first tau repeat domain and the second tau repeat domain form in a subset of the seeded population of cells to produce an aggregation-positive population of cells; and (f) determining abundance of each of the plurality of unique guide RNAs in the aggregation-positive population of cells identified in step (e) relative to the genetically modified population of cells in step (c), wherein enrichment of a guide RNA in the aggregation-positive population of cells identified in step (e) relative to the cultured population of cells in step (c) indicates that the gene targeted by the guide RNA is a genetic modifier of tau aggregation, wherein disruption of the gene targeted by the guide RNA enhances tau aggregation. (a) providing a population of cells comprising a Cas protein, a first tau repeat domain linked to a first reporter, and a second tau repeat domain linked to a second reporter, wherein the cells are mammalian cells, wherein the first reporter and the second reporter are fluorescent proteins, and wherein the first reporter and the second reporter are a fluorescence resonance energy transfer (FRET) pair; wherein the cells are mammalian cells, wherein the first reporter and the second reporter are fluorescent proteins, and wherein the first reporter and the second reporter are a fluorescence resonance energy transfer (FRET) pair; (b) introducing into the population of cells a library comprising a plurality of unique guide RNAs that target a plurality of genes; (c) culturing the population of cells to allow genome editing and expansion, wherein the plurality of unique guide RNAs form complexes with the Cas protein, and the Cas protein cleaves the plurality of genes resulting in knockout of gene function to produce a genetically modified population of cells; (d) contacting the genetically modified population of cells with a tau seeding agent to produce a seeded population of cells, wherein step (d) comprises culturing the genetically modified population of cells in the presence of conditioned medium harvested from cultured tau-aggregation-positive cells in which a tau repeat domain stably presents in an aggregated state, wherein the conditioned medium was harvested after being on confluent tau-aggregation-positive cells for 1 to 7 days; (e) culturing the seeded population of cells to allow tau aggregates to form, wherein aggregates of the first tau repeat domain and the second tau repeat domain form in a subset of the seeded population of cells to produce an aggregation-positive population of cells; and (f) determining abundance of each of the plurality of unique guide RNAs in the aggregation-positive population of cells identified in step (e) relative to the genetically modified population of cells in step (c),