Analysis of tumor proliferation using Ki67 staining in zebrafish MDA-MB-231 xenograft models has also been used in studies of cancer cell migration [48], and fluorescence sensing of caspase-3 expression has been used to analyze the role of natural killer cells in promoting apoptosis in Tg (fli1:EGFP) zebrafish embryos [49]. The gene discussed is MKI67; the disease is cancer.