Septins Provide Microenvironment Sensing and Cortical Actomyosin Partitioning in Motile Amoeboid T Lymphocytes

Abstract

The all-terrain motility of lymphocytes in tissues and tissue-like gels is best described as amoeboid motility. For amoeboid motility, lymphocytes do not require specific biochemical or structural modifications to the surrounding extracellular matrix. Instead, they rely on changing shape and steric interactions with the microenvironment. However, the exact mechanism of amoeboid motility remains elusive. Here we report that septins shape T cells for amoeboid motility. Specifically, septins form F-actin and alpha-actinin-rich cortical rings at the sites of cortex-indenting collisions of T cells with the extracellular matrix. Cortical rings compartmentalize cells into chains of spherical segments that are spatially conformed to the available lumens, forming transient hourglass-shaped steric locks onto the surrounding collagen fibers. The steric lock facilitates pressure-driven peristaltic propulsion of cytosolic content by individually contracting cell segments. Our results demonstrate that septins provide microenvironment-guided partitioning of actomyosin contractility and steric pivots for amoeboid motility of T cells in tissue-like microenvironments. GLOSSARYO_LISteric interactions - interactions by the means of their spatial collision dependent on objects shapes. C_LIO_LISteric guidance - cell navigation within crowded 3D environments, determined by the available passages around and between steric hindrances. C_LIO_LIPeristaltic treadmilling - locomotion mode by the means of a repeated sequence of polarized cell cortex extension, stabilization, and retraction, accompanied by translocation of nucleus and cytoplasm via circumferential cortex contractility. C_LI Significance StatementT cells can be highly motile, searching for cognate antigens or better yet targets in chimeric antigen receptor therapy settings. However, mechanisms of motility remain elusive for T cells migrating in structurally and biochemically diverse tissues. Here we address one pivotal question of basic and clinical immunology - How T cells achieve the all-terrain motility? Here we decipher and report septin-based T cell motility in a 3D tissue-like environment. Specifically, we show that septins facilitate cell morphological responsiveness to the steric obstacles, i.e., collagen fiber-wise partitioning of actomyosin cortex contractility and cell-obstacle steric interactions. These responses coordinate peristaltic propulsion of the lymphocytes cytosolic content along its individually contracting cell segments, forming the obstacle-avoiding motility, i.e., circumnavigation, shared across various tested lymphocytes.