CRISPR screen

A CRISPR screen asks thousands of genes the same question at once: “If I switch you off, what changes?” Instead of editing one gene and watching the result, scientists edit a different gene in each cell across a huge population, then see which edits make cells grow, die, or behave differently.

In a typical pooled screen, a library of guide RNAs — often one or more targeting every gene in the genome — is delivered so that each cell receives just one guide and knocks out (or activates, or represses) a single gene. The cells are then put under a chosen pressure, such as a drug. By sequencing the guide RNAs at the start and end and counting which become enriched or depleted, researchers infer which genes helped or hindered survival.

Screens turn genetics into a large-scale, systematic search and have revealed drug targets, essential genes, and resistance mechanisms. Their honest limits include incomplete or off-target editing, guides of uneven efficiency, and the need for careful statistics — a hit is a hypothesis to validate, not yet a proven answer.