Abstract
The material properties of tissues and their mechanical state is an important factor in development, disease, regenerative medicine and tissue engineering. Here we describe a microrheological measurement technique utilizing aggregates of microinjected ferromagnetic nickel particles to probe the viscoelastic properties of embryonic tissues. Quail embryos were cultured in a plastic incubator chamber located at the center of two pairs of crossed electromagnets. We found a pronounced viscoelastic behavior within the ECM-rich region separating the mesoderm and endoderm in Hamburger Hamilton stage 10 quail embryos, consistent with a Zener (standard generalized solid) model. The viscoelastic response is about 45% of the total response, with a characteristic relaxation time of 1.3 s.
Highlights
Tissues are physical bodies, their formation necessarily involves controlled generation and relaxation of mechanical stresses (Preziosi et al, 2010)
The incubator chamber consists of two heated indium tin oxide (ITO) glass surfaces that enclose a 35mm dish (Figures 1A,B)
Temperature was controlled by heating currents within the ITO surfaces, feedback was provided by a thermometer probe immersed in the water bath surrounding the agarose bed
Summary
Their formation necessarily involves controlled generation and relaxation of mechanical stresses (Preziosi et al, 2010). Tissue cells are known to generate mechanical stresses by actin-myosin contractility, relying on non-muscle Myosin II, with upstream regulators coordinated through a spatial and temporal activity of rho GTPases such as RhoA (Ridley et al, 2003). The relaxation of mechanical stresses involves the disruption of cellcell connections, often accompanied by changes in cell neighbors (Forgacs et al, 1998; Smutny et al, 2017; Petridou et al, 2019). While this process is less understood on the molecular level than acto-myosin contractility, the spatio-temporal regulation for both force generation and relaxation are important to shape the embryonic tissues. The pulsatile nature of tissue movements is evident in the ECM displacements recorded within avian embryos (Szabó et al, 2011)
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