Zebrafish screen for potential T-ALL therapeutics. (A) Adults carrying a transgene that fluorescently labels T cells (lck:EGFP) are mated. Resulting embryos have fluorescent T cells in the thymus (green oval in magnified embryo schematic). Immature T cells in embryos are posited to be similar to malignant lymphoblasts. (B) Five-day-old embryos are arrayed into 96-well plates and incubated with different compounds from a small molecule library. Forty-eight hours later, embryos are observed to determine general health, and examined for normal (left embryo) or decreased (right embryo) T-cell numbers, visible as reduced fluorescence. (C) Effective compounds are further verified and tested in follow-up assays.