Toll-like receptors in epithelial mechanics and surveillance

Toll-like receptors (TLRs) were first identified as developmental cues that establish the dorsal-ventral axis in Drosophila. This discovery was followed by the recognition of their central role in invertebrate and vertebrate innate immunity. Here we review an additional set of discoveries that establishes the role of TLRs in epithelial tissue dynamics and surveillance in Drosophila. A growing body of work reveals that, largely independent of their canonical signalling, TLRs guide tissue mechanics. Spatial patterns of TLR localisation control collective cell movements and large-scale morphogenesis by modulating cell contractility. Intriguingly, the same TLRs also enable tissues to recognise and remove unfit or misplaced cells, revealing their essential function in tissue surveillance during development. Across these contexts, TLRs act as sensors that integrate positional information, mechanical forces, and cell identity. By tracing the path from early embryonic patterning to immunity, mechanics and finally tissue surveillance, this review highlights how the evolutionarily conserved TLR family continues to refine our understanding of how tissues shape, maintain, and protect themselves.