Mechanical tension and movement in the chick blastoderm as studied by real-time image analysis

The mechanical activity of embryonic cells was studied in vitro in whole gastrulating chick blastoderms by means of video-image analysis. Displacements of identified points were recorded and interpreted in terms of deformation and active movement. From the deformations of the vitelline membrane to which blastoderms attach by the edge cells, it was deduced that the blastoderms developed and maintained a tension of 1-1.2 X 10(4) dyn/cm2. This tension was generated by a radial contraction of cells situated in the area opaca. This contraction stretched the area pellucida where the embryogenesis took place. Additional experimentally induced distension of the vitelline membrane affected the migration of the edge cells and the formation of the primitive streak. Decrease in temperature, anoxia, colchicine, and cytochalasin B relaxed the tension in the membrane but resulted in different deformation patterns in the blastoderm. A focalized electrical stimulation led to local contractions of cells in all regions of the blastoderm except the edge cells. The tension within the contracted cells increased up to 4 X 10(4) dyn/cm2. In the area pellucida, movements of migrating mesoblastic cells showed periodic saccades lasting about 5 min. Repetitive electrical stimuli applied at the same period induced ectopic migration of cells in the area pellucida but not in the area opaca. These results are discussed with respect to factors possibly modulating the activity of embryonic cells during early morphogenesis.