The 3D micro- and nanostructure of the apical extracellular matrix in <i>Drosophila</i>

Abstract The apical extracellular matrix (aECM) serves as a dynamic scaffold, orchestrating tissue growth, cellular communication, and wound repair, and thus functions as a powerful biomaterial. In this study, we explored the intricate three-dimensional landscape of the Drosophila larval aECM using advanced 3D Volume electron microscopy. This technique opens a window into understanding and mimicking the diversity of aECM surfaces and architectures of the exoskeletal cuticles. We reconstructed the striking forms of denticles, hairs, and sensory organs, including double sensilla and Keil’s organs, at the epidermal surface. Our reconstructions brought the larval tracheal system and the sponge-like felt chamber (Filzkörper) of the spiracles into sharp relief, revealing a labyrinth of tiny cavities surrounding a central tube that extends from the posterior opening to the tracheal lumen. When examining the ultrastructure of transport-active anal pad cells, we discovered an inverted pattern of cuticular pore-canal structures, which supports their suggested role in osmoregulation across the aECM. Our findings further suggest that ordinary epidermal cells weave an intricate network of pore canals, enabling the orchestration of material distribution throughout the entire aECM. Moreover, we reconstructed tendon cells and chordotonal organs that form a branching network of numerous filamentous intracuticular fibers that weave through the aECM, linking the exoskeleton to muscles and sensory organs. By thoroughly mapping the intricate ultrastructural features of the aECM, this study opens new avenues for exploring how its protective, mechanical, and sensory roles intertwine, inspiring the next generation of tailor-made biomimetic materials.