A role for LIMA1 in the assembly of actin bundle-supported protrusions

Actin bundle-supported membrane protrusions contribute to a range of physiological functions across cell types. An interesting case is the tuft cell, which assembles exaggerated microvillus-like protrusions that support chemosensory functions in the intestinal tract. Tuft cell protrusions are supported by large core actin bundles; several F-actin bundlers are expressed in tuft cells, and these exhibit regionalized localization along the core bundle axis. Uniquely, LIM domain and actin binding 1 (LIMA1) is restricted to the basal, rootlet ends of these bundles. How LIMA1 impacts protrusion formation and core bundle architecture remains unclear. Here, we leveraged multiple forms of microscopy to examine the impact of LIMA1 on the actin cytoskeleton in epithelial and nonepithelial models. Our findings indicate that LIMA1 expression is sufficient to drive the elongation of microvilli in epithelial cells, as well as the formation and stabilization of exaggerated filopodia in a non-epithelial context. Importantly, we found that individual filopodia in LIMA1-overexpressing cells exhibit merging dynamics, which enable the formation of large core bundles from smaller precursors. These data indicate that LIMA1 exerts potent effects on rootlet actin architecture and is well positioned to support the formation and maintenance of large core actin bundles, like those assembled by tuft cells.