Evaluation of Wnt targets during intestinal development and carcinogenesis

Aims: Activation of the canonical Wnt pathway is a indispensable for intestinal development, and also observed during intestinal carcinogenesis. In mice, conditional ablation of APC in the intestine leads to rapid perturbation of differentiation and proliferation.

Methods: Expression array analysis was performed at day 5 after induction to monitor early changes following loss of APC in vivo. Of the genes found to be upregulated here, 150 were further studied by in situ hybridization in intestines and whole embryos.

Results: Beneath typical Wnt target genes as Cyclin D1, new targets were identified which exhibited expression patterns according to expected Wnt activity. Distinct expression patterns were observed, ranging from crypt restricted expression, adenoma specific expression crypt – adenoma expression to gradient expression in the crypt – villus axis. Other genes were expressed during embryonic development and adenoma development. Genes expressed in crypts and tumors included transcription factors (Sox9, Sp5, Foxa1, FoxA3, Cbfb, Ap4), cell cycle associated proteins (Mad1l1, Cdc37, Mcm3, CDT), factors regulating development (diaphanous, timeless, schlafen), and numerous proteins of yet unknown function. Biochemical evaluation in TOP-FOP assays revealed that some of these interfere with Wnt pathway, indicating positive or negative regulating feedback loops.

Conclusion: This approach identified several yet unknown targets of the Wnt pathway which might be important during development and carcinogensis of the intestine, which will be further validated by conditional ablation in mice.