Estimating the Mechanical Properties of Lytechinus Variegatus Eggs Through Membrane Blebbing

Undergraduate #8
Discipline: Biological Sciences
Subcategory: Cell and Molecular Biology

Darnell Dinwiddie - Tuskegee University
Co-Author(s): Emily Williams, Old Dominion University Jian Du and David Carroll

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Cells must withstand many changes during their lifespans. To meet these challenges, they must respond to environmental variables that include pressure, temperature, viscosity, and flow. In many cases, the features of the cell that allow them to handle these physical parameters are unknown. This study will utilize eggs from the sea urchin Lytechinus variegatus to address this issue. These eggs are made of two outer layers, a soft, permeable membrane surrounding a stiff, actin-rich cortex. These layers are encased in a glucose covering, the vitelline envelope. The inside contains the fluid cytosol, which itself is not homogenous throughout. The physical parameters of these compartments will be estimated computationally and tested using a feature of the cell membrane called blebbing. Blebbing occurs in cells naturally during apoptosis, cytokinesis, cell spreading, etc., but may also be induced artificially by destabilizing the cell cortex using the laser scanning confocal microscope. The process involves local detachment of the cell cortex from the membrane followed by the flow of cytosol into the area, resulting in the expansion of the cell membrane. The flow of cytosol is caused by the pressure difference in the cell, resulting from the lack of cortex in the area of detachment. As the bleb reaches a steady-state, the cortex reforms, and the bleb detaches or detracts.

This study will use induced blebbing to gain more information on the mechanical properties of cells, such as: viscosity, tension, pressure, etc. Previous studies have estimated some of these parameters, but we hope to quantify them more accurately. The results of our experiments indicate that the cell cortex contributes necessary tension and that the cells do not bleb once they reach pressure equilibrium. Pressure is important in bleb formation. We used 50% sea water because it exerts less pressure, forming blebs until the cell has equilibrated.Tension is also a vital factor. The cortex, membrane, and Vitelline Envelope all produce tension, holding the cytosol in. Our experiment shed light on the adaptability of Lytechinus variegatus eggs and cells as a whole. Even after damage was induced, cells often returned to their previous state.

Funder Acknowledgement(s): REU NSF

Faculty Advisor: David Carroll,