TGIF1 and breast cancer: To investigate whether Tgif1 in osteoblasts is involved in regulating the osteoblast-mediated increase in breast cancer cell migration, we induced breast cancer cell migration with conditioned medium collected from osteoblasts that were isolated from mice bearing a germ line deletion of Tgif1 (Tgif1−/−) or from control littermates (Tgif1+/+).