Hbs and Rst adhesion molecules provide a regional code that regulates cell elimination during epithelial remodelling

Abstract

Cell-cell interactions and mechanical forces are fundamental in shaping epithelial tissue architecture. For example, tissue compression promotes cell elimination by downregulating compaction-sensitive EGFR/ERK signalling. However, a subgroup of cells that are eliminated do not show EGFR/ERK downregulation, suggesting the involvement of additional mechanisms. Here, we conducted a multi-step RNAi screen in the Drosophila notum and identified 47 diverse regulators of epithelial remodelling. Among them, we focused on two membrane proteins, Hibris (Hbs) and Roughest (Rst), which mediate heterophilic cell adhesion. We show that Hbs and Rst exhibit region-specific expression patterns in the developing notum, showing elevated protein levels in zones of cell survival and reduced expression in regions undergoing cell pruning. Uniform knock-down of hbs and rst or homogenous overexpression of hbs, disrupts normal cell elimination during morphogenesis and results in adult tissue malformations. Remarkably, local suppression of Hbs and Rst in Hbshigh /Rsthigh territories triggers ectopic cell elimination, indicating that a surface code defined by Hbs/Rst can instruct cell removal. We further demonstrate that Hbs, but not Rst, is regulated by compaction-sensitive EGFR signalling, positioning Hbs as a potential integrator of mechanical cues and cell property signals, possibly via its interaction with Rst. These findings uncover a novel adhesive code that shapes the thorax midline and potentially other organs.