(129f) Modeling the Ermad-Cortical Actin Interface to Elucidate Endodermal Cell Blebbing Mechanics

Migrating cells exhibit many different membrane protrusions as they crawl along a substrate. One of these types of protrusions, known as blebs, occurs when there is a local detachment between the cell’s actin cortex and plasma membrane. In preliminary experiments, we found a correlation between blebbing frequency and expression of membrane-to-cortex attachment (MCA) proteins during early endoderm development in zebrafish embryos. Still, the mechanics underlying the attachments themselves is unclear. To understand the role of MCAs in bleb formation, we present an in vitro model to quantify MCA strength directly. Specifically, in this study, we present results on the strength of attachment between the actin-binding domain of the MCA protein Ezrin, known as ERMAD, and cortical actin. To validate and characterize the ERMAD-actin in vitro interface we combined quartz crystal microbalance with dissipation (QCM-D), confocal epifluorescence microscopy, and the surface forces apparatus (SFA) to quantify ERMAD surface density, visualize cortical actin architecture, and quantify binding strength between ERMAD and cortical actin. QCM results indicate that ERMAD surface density is comparable to that reported for zebrafish mesendoderm progenitor cells. Confocal epifluorescence microscopy reveals that surface-immobilized actin filaments are linear and in the micrometer length scale. SFA shows that the ERMAD-actin interaction is adhesive. These results provide insights into the individual components of both ERMAD and actin interfaces which can be used as a foundation to further explore the interaction between these components, deepening our understanding of how the inner mechanics of the actin cytoskeleton and plasma membrane, i.e., blebbing, moderate coordinated processes like cell contractility and cortical tension.