Implantation of primary human tumour cells into the zebrafish liver. (A-D) Organotopic implantation of primary tumour cells into the liver of larvae of Fli-1 zebrafish. Representative examples of zebrafish at 5 days of development injected with primary normal pancreatic cells (NPC) and with primary dissociated pancreatic tumour cells (A and C, respectively) are shown. The same fish are depicted at 1 day post injection (1 dpi). While normal pancreatic cells remained at the site of implantation in the liver (B), pancreatic tumour cells invaded the embryo and formed distant metastases, indicated with arrows (D). Scales indicated are: A-D 300 μm. Individuals were followed for up to 7 dpi and untransformed control cells never invaded the host embryos and remained in the liver for the entire observation period (data not shown). Image E shows an example of proliferating tumour cells of a transplanted pancreatic tumour fragment on consecutive days. The single cell on the right seen at 1 day post transplantation is divided into two daughter cells on 2 dpt and four cells are visible at 3 dpt. Dual colour laser scanning confocal images of the Fli-1 zebrafish are shown and in the smaller insert the red fluorescence of the CM-Dil labelled tumour cells can be seen.