Fig. 2

Notch-dependent intercellular communication in the segmentation clock. a: Cell-transplantation assay at the blastula stage. b: Donor cells that constitutively expresses DeltaC due to a morpholino-knockdown of Her. c: Effects of her-MO cells on the transcription of her1 (left) and on the segmentation points (right). The timing of her1 transcription is locally advanced in the area near to the explants in the posterior PSM. The nuclei, her1 mRNA, and explants are stained in red, green, and blue, respectively. Arrowheads indicate nuclear her1 cells, the phase of which is advanced by transplantation. This effect results in a segment-shift phenotype. The segment positions are anteriorly shifted on the transplanted side (arrows). Donor cells are in red and the dashed line indicates the last normally formed segment border. Scale bar = 20 μm. d: 1-D simulation of oscillating PSM cells (dots). Snapshots of the calculated results in the 1st (up) and 10th-round of oscillation (down) are shown. An actively signaling cell is represented by a red arrow. The active signal from the transplanted cell influences the adjacent cell to accelerate the oscillating. After 10 rounds of oscillation, the oscillation phase of the red PSM cell advances by 13.2%, as compared with the green PSM cell that is located far from the signaling cell. This effect is transmitted in succession, and results in the phase-shift of relatively distant cells, although the effect is still locally limited. e: The smaller somite (red solid box) is formed by the accelerated oscillation (red line). The spatial pattern of clock oscillation (lines at the bottom) is translated according to the clock-and-wavefront mechanism.