Fig. 10. Summary and model for the action of Notch signaling. (A) The signal (arrows) emanating from the posterior border cells and acting on the anterior border cells is designated as the ‘segmenter’. See text for detailed explanation. Lfng mRNA normally located posterior to the line 0 is not shown to allow the molecular events at –1 to be clearly represented. (B) Two models proposing a mode of Notch action in somite boundary formation analogous to its action in Drosophila. See text for details.