Investigating the Molecular Architecture of a Cytoskeletal Superstructure in the Intestinal Tuft Cell

Abstract

Tuft cells are a rare epithelial cell type that play important roles in sensing and responding to luminal antigens. A defining morphological feature of this lineage is the actin-rich apical ‘tuft’, which contains large fingerlike protrusions. However, details of the cytoskeletal ultrastructure underpinning the tuft, the molecules involved in building this structure, or how it supports tuft cell biology remain unclear. In the context of the small intestine, we found that tuft cell protrusions are supported by long core bundles that consist of F-actin crosslinked in a parallel and polarized configuration; they also contain a tuft cell-specific complement of actin-binding proteins that exhibit regionalized localization along the bundle axis. Actin-crosslinking protein LIMA1 is uniquely localized to the rootlets of tuft cell core actin bundles. Using cell culture models to determine the impact of LIMA1 on actin architecture, we found that expression of LIMA1 is sufficient to drive the formation of exaggerated filopodia due the stabilization of actin bundles from LIMA1 and its protective effect against actin depolymerization. Remarkably, the loss of LIMA1 in mice compromised the integrity of tuft cell rootlets providing evidence that LIMA1 supports the integrity of rootlet actin architecture in tuft cells. These rootlets are co-aligned with a highly ordered microtubule network, making the resulting cytoskeletal superstructure well positioned to support subcellular transport and, in turn, the dynamic sensing functions of the tuft cell that are critical for intestinal homeostasis.