Session: Government Agency Student Posters

Paper Number: 173603

Collective Migration of Multicellular Clusters via Marangoni Surface Tension Gradients 

Epithelial cells establish polarity by trafficking specific proteins to the apical or basal surfaces, a process essential for maintaining physiological function. Disruption of this polarity is increasingly recognized as a hallmark of cancer progression, with recent studies identifying multicellular aggregates exhibiting "apical-out" polarity in human carcinomas that may facilitate metastatic dissemination. Studies show that when epithelial cells derived from glandular tissues are cultured in a three-dimensional soft extracellular matrix (ECM), they spontaneously organize into spheroid structures known as acini, comprising a monolayer of polarized cells surrounding a pressurized fluid-filled lumen. We have previously demonstrated that acinar eversion of hollow cellular aggregates form structures with apical-out polarity. However, the subsequent behavior and migratory mechanisms of these structures remained unexplored.

To address this gap, we employed high-resolution live imaging to track the fate of everted acini within three-dimensional extracellular matrices (ECM). MDCK cells stably expressing GFP-podocalyxin were cultured using an overlay method, embedding the cells between two layers of Matrigel. The culture substrate was first coated with growth factor-reduced Matrigel to create a cushioning layer, followed by seeding cells suspended in diluted Matrigel onto this layer. Fluorescent microbeads were incorporated into the top layer for visualization of matrix dynamics. Live imaging was performed using confocal microscopy over 24–72 hours, and quantitative analysis including Mean Square Displacement (MSD) analysis and particle image velocimetry (PIV) were performed using MATLAB to assess cell and matrix movement.

Our results revealed that acini that did not evert after Rho activation remained stationary. However, following eversion, acini exhibited robust collective migration over several days, frequently merging with neighboring aggregates to form larger multicellular structures. Migration was characterized by a distinct "run-and-tumble" pattern, consisting of alternating phases of persistent, directed movement and directional changes. Tracking of microbeads embedded in the ECM revealed a rearward flow and accumulation of matrix material at the trailing edge of migrating acini, indicating active matrix remodeling. Notably, the motion correlated with a front-to-back gradient of the apical marker podocalyxin and a back-to-front gradient of phosphorylated myosin, with podocalyxin excluded from myosin-rich regions. This surface tension gradient, known as "Marangoni stress" in fluid mechanics, drove a characteristic cell flow, with outer cells moving rearward and inner cells recirculating forward. Experimental measurements of aggregate speed versus gradient magnitude closely matched predictions from our mathematical model accounting for Marangoni stress-driven motility. Further we found that blocking β1 integrin, inhibiting Rac1 activity, or decreasing myosin contractility significantly reduced the migratory behavior of everted structures, indicating these factors' importance in migration following eversion.

Our findings uncover a novel, contractility-dependent mechanism of collective migration in apical-out acini, governed by run-and-tumble dynamics and surface tension gradients. This mode of motility may mirror the behavior of apical-out tumor spheres in vivo and contribute to the metastatic spread of epithelial cancers.

Presenting Author: Hailee Patel Texas A&M University

Presenting Author Biography: I'm a fourth year Ph.D. candidate at the department of biomedical engineering at Texas A&M University. I work in the cancer mechanobiology lab, and my work focuses on the migration dynamics of everted acini in 3D gels.

Authors:

Hailee Patel Texas A&M University
Richard Dickinson University of Florida
Tanmay Lele Texas A&M University