Zebrafish reporter lines reveal in vivo signaling pathway activities involved in pancreatic cancer.

Pancreatic adenocarcinoma, one of the worst malignancies of exocrine pancreas, is a solid tumor with increasing incidence and mortality in industrialized countries. It is usually driven by oncogenic Kras point mutations and evolves into a highly aggressive metastatic carcinoma due to secondary gene mutations and specific signaling pathways unbalance. To examine in vivo the effects of KrasG12D during pancreatic cancer progression and time correlation with cancer signaling pathways activities, we have generated a zebrafish model of Pancreatic adenocarcinoma in which eGFP-KrasG12D expression was specifically driven to the pancreatic tissue by using the GAL4/UAS conditional expression system. Outcrossing the inducible oncogenic KrasG12D line with transgenic zebrafish reporters harboring specific signaling responsive elements of transcriptional effectors, we were able to follow TGFβ, Notch, Bmp and Shh activities during tumor development. Zebrafish transgenic lines expressing eGFP-KrasG12D showed normal exocrine pancreas development till 3 weeks post fertilization (wpf). From 4 to 24 wpf we observed several degree of acinar lesions, characterized by an increase of mesenchymal cells and mixed acinar/ductal features followed by progressive bowel and liver infiltrations finally bringing to highly aggressive carcinoma. Moreover, live imaging analysis of the exocrine pancreatic tissue revealed an increasing number of Kras positive cells and progressive activation of TGFβ; and Notch pathways. Increase of TGFβ, following KrasG12D activation, was confirmed in a concomitant model of medulloblastoma (MDB). Notch and Shh signaling activities during tumor onset were different between MDB and pancreatic adenocarcinoma indicating a tissue specific regulation of cell signaling pathways. Moreover, our results shows that a living model of pancreatic adenocarcinoma joined with cell signaling reporters is a suitable tool to describe in vivo the signaling cascades and molecular mechanisms involved in tumor development and a potential platform to screen for novel oncostatic drugs.