Probing the Canonicity of the Wnt/Wingless Signaling Pathway [STARR-seq]. Drosophila melanogaster

The hallmark of canonical Wnt signaling is the transcriptional induction of Wnt target genes by the beta-catenin/TCF complex. Several studies have proposed alternative interaction partners for beta-catenin or TCF, but the relevance of potential bifurcations in the distal Wnt pathway remains unclear. Here we study on a genome-wide scale the requirement for Armadillo (Arm, homolog of beta-catenin) and Pangolin (Pan, Drosophila’s TCF) in the Wnt/Wingless (Wg)-induced transcriptional response of Drosophila Kc cells. Using somatic genetics, we demonstrate that both Arm and Pan are absolutely required for mediating activation and repression of target genes. Furthermore, by means of STARR-sequencing we identified Wnt/Wg-responsive enhancer elements and found that all responsive enhancers depend on Pan. Together, our results confirm the dogma of canonical Wnt/Wg signaling and argue against the existence of distal pathway branches in this system. Overall design: STARR-seq was performed in wild type Drosophila Kc167 cells and Pangolin mutated Drosophila Kc167 cells treated with CHIR99021 or DMSO in two replicates.