Research Projects

Wnt signaling pathways, triggered by secreted Wnt ligands, play a central role in numerous cellular and developmental processes. Dysregulation of Wnt signaling is linked to developmental disorders and diseases, including cancer (Nusse and Clevers, 2017; Zhan et al., 2017). Wnt ligands activate signaling by binding to Frizzled (Fz) receptors, initiating multiple downstream signaling cascades. These pathways are broadly classified into canonical (β-catenin-dependent) and non-canonical (β-catenin-independent) signaling. More recently, Wnt proteins have been found to regulate other pathways, including the Hippo-YAP/TAZ and JNK signaling pathways, collectively referred to as ‘alternative Wnt signaling’ (Kluge et al., 2024; Park et al., 2015). While the molecular mechanisms of canonical Wnt signaling have been extensively studied, alternative Wnt pathways remain less understood despite their significance in development and disease. A key unanswered question is how different Wnt–Frizzled interactions elicit distinct cellular responses. In this study, we aim to investigate the role of the Frizzled2 (Fz2)-regulated alternative Wnt pathways in competitive cell interactions, using Drosophila epithelial tissues as a model. Drosophila offers a simplified yet highly conserved system for studying Wnt signaling. Specifically, we will explore how Fz2 expression affects non-autonomous signaling, such as cell survival and death. The proposed study is driven by our recent observations that clonal overexpression of Fz2 in developing epithelial tissues produces “super-competitor” cells. These cells overproliferate by outcompeting and inducing apoptosis in neighboring wild-type cells. This effect involves non-autonomous JNK pathway activation in adjacent cells, which appears to be independent of canonical β-catenin signaling. In contrast, overexpressing hyperactive β-catenin triggers only modest overgrowth and autonomous JNK activation. Similar effects were seen in larval epidermal cells (LECs), where Fz2 overexpression caused neighboring histoblast cell death and disrupted abdominal patterning in adult flies. These findings suggest Fz2 may activate alternative Wnt pathways separate from canonical signaling. To dissect this mechanism, we will focus on the role of the transcription factor Yorkie (Yki) and the Toll pathway ligand Eiger, both potential mediators of JNK activation and apoptosis. We will utilize the abdominal phenotype caused by Fz2 overexpression to perform RNAi-based rescue screens to identify key mediators. Activation of alternative pathways will be measured using gene reporters and qRT-PCR. We also aim to perform a structure-function analysis of the Fz2 receptor to identify motifs specific for canonical and alternative signaling. Initially, we will assess the available point mutants of Fz2 that are defective in canonical signaling for their ability to trigger non-canonical responses such as cell competition and non-autonomous apoptosis. Alternatively, we will apply forward genetic approaches to identify new mutations that impair the activation of the involved alternative pathway. In summary, this research aims to define how Frizzled2 regulates non-autonomous cell behavior through alternative Wnt pathways. By combining genetic, imaging, and molecular tools in Drosophila, we aim to reveal how specific receptor-level signals direct distinct outcomes. These insights will have broader implications for understanding tissue development, regeneration, and tumor progression