Frizzled1 and Frizzled2 are not redundant for competitive survival under low-Wingless levels in the developing <i>Drosophila</i> wing epithelium

In the <i>Drosophila</i> wing epithelium, canonical Wnt signalling is activated by the gradient of secreted Wingless protein (Wnt1 homolog), which interacts redundantly with the Frizzled1 and Frizzled2 receptors. While sharing overlapping functions, these receptors also have distinct non-canonical roles and exhibit differential expression patterns along the Wingless gradient. Moreover, Frizzled2, unlike Frizzled1, is thought to be essential for sustaining low-level Wingless signalling and promoting cell survival in the absence of the ligand. This raises the possibility of the two receptors acting differently along the Wingless gradient. In this study, we investigated the role of these receptors in cell survival across varying Wingless levels. We find that the loss of Frizzled2 in cells at a distance from the Wingless-producing cells-where Wingless levels are low-leads to competitive elimination of cells. In contrast, Frizzled1 is dispensable for cell survival, regardless of distance from the Wingless source. Our findings show that Frizzled2 is essential for competitive cell survival under low-Wingless conditions, and the two receptors are not equally redundant across the Wingless concentration gradient, providing insight into a mechanism for spatial and temporal precision in developmental signalling.