Abstract
We estimated stress distribution in fresh Xenopus laevis embryos at tailbud stage by measuring surface topography and stiffness distribution on a section of embryonic tissues. When an elastic body having residual stress is cut, pops and dents appear on the section according to the direction and magnitude of the residual stress. Stress distribution necessary to restore the section to flat plane is considered to be the residual stress distribution. In reality, however, fresh embryo is very soft and sticky, and its contents flow out easily after being cut. To overcome these problems, we constructed a special setup in which tailbud embryos were cut perpendicular to the median line in Steinberg's solution with fine platinum wire electrified with high-frequency current and topography of the section was measured within 30 s with a laser-scanning microscope. We found that three sites of the section, i.e., neural tube, notochord and ventral tissue, protruded by 40-80 μm from surrounding tissues at stages 33-34. We then developed an indentation device to measure mechanical properties on the section under a microscope, and found that Young's modulus was 〜4 kPa for neural tube and 〜0.5 kPa for ventral tissue. Our findings suggest that neural tube, notochord and ventral tissue produce the force to elongate the tailbud embryo. Multiple elongation sites may prevent the embryos from bending during body elongation process that might occur when the body elongation was driven by a single site.
