Meeting Abstract

P2.42  Monday, Jan. 5  Slicing, shocking, and sucking on embryos to differentiate active and passive mechanical behaviors of developing tissues. VON DASSOW, M.*; DAVIDSON, L.A.; Univ. of Pittsburgh; Univ. of Pittsburgh mvondass@yahoo.com

A fundamental problem in the biomechanics of morphogenesis is differentiating active force generating processes from passive viscoelastic properties of embryonic tissues. We use micro-aspiration to assay the apparent stiffness of gastrulating Xenopus laevis embryos in vivo. We apply suction to a patch of the embryo surface through a 125 micrometer diameter channel and measure the resulting deformation. Previously we observed that these tissues occasionally contract with sufficient force to counter the applied suction (5.4 Pa) over a period of one to several minutes. Rapid, stochastic contractions are also visible in time-lapse videos of embryos that are minimally manipulated, just constrained enough to stay in place. If we could experimentally induce contractions it would open up new means to investigate the relations between active contractility and passive viscoelasticity, and to identify potential regulators of contractility in embryos. We noticed that wounding stimulates contraction in both the wounded embryo and adjacent embryos. Hence, a diffusible factor released by wounding can induce contraction. We wondered if electrical stimulation could also cause contractions. The micro-aspirator channel can serve as an electrode so it allows measurement of apparent stiffness and simultaneous electrical stimulation. Stimulating the ~125 micrometer diameter aspirated tissue with ~0.1 mA for 0.05 to 0.4 ms induced strong contractions. Peak contraction occurred ~1 min after stimulation, with relaxation occurring over the following 1 to 2 minutes. Hence, we can now combine mechanical testing with acute control of contractility, opening up new avenues to experimentally differentiate active and passive mechanical behaviors in living, developing embryos.