Intestinal tuft cells assemble a cytoskeletal superstructure composed of co-aligned actin bundles and microtubules

Abstract

All tissues consist of a distinct set of cell types, which collectively support organ function and homeostasis. Tuft cells are a rare epithelial cell type found in diverse epithelia, where they play important roles in sensing antigens and stimulating downstream immune responses. Exhibiting a unique polarized morphology, tuft cells are defined by an array of giant actin filament bundles that support ~2 microns of apical membrane protrusion and extend over 7 microns towards the perinuclear region. Despite their established roles in maintaining intestinal epithelial homeostasis, tuft cells remain understudied due to their rarity. Details regarding the ultrastructural organization of the tuft cell cytoskeleton, the molecular components involved in building the array of giant actin bundles, and how these cytoskeletal structures support tuft cell biology remain unclear. To begin to answer these questions, we used advanced light and electron microscopy to perform quantitative morphometry of the small intestinal tuft cell cytoskeleton. We found that tuft cell core bundles consist of actin filaments that are crosslinked in a parallel barbed-end out configuration. These polarized structures are also supported by a unique group of tuft cell enriched actin-binding proteins that are differentially localized along the giant core bundles. Furthermore, we found that tuft cell actin bundles are co-aligned with a highly ordered network of microtubules. Tuft cells assemble a cytoskeletal superstructure that is well positioned to serve as a track for subcellular transport along the apical-basolateral axis and in turn, support the dynamic sensing functions that are critical for intestinal epithelial homeostasis.