Fig. 10. Model of molecular interactions in HER-linked Delta/Notch oscillator: cell-autonomous and non-autonomous, or phase-adjusting aspects. Proposed molecular interactions of the core segmentation oscillator are represented in diagrammatic form inside an abstracted PSM cell. Normal type and capital letters indicate proteins and lowercase italics indicate genes and RNA. Black lettering and arrows indicate high levels or activity, whereas gray represent low levels or activity. Open ‘B’ arrowhead represents the basal level of stimulus to the dlc gene throughout the PSM, revealed in the absence of oscillator activity. The Notch receptor is ubiquitously expressed in the PSM. This core oscillator mechanism is hypothesized to run throughout the PSM, but may be modified by other factors at different locations in the PSM, for example, DeltaD in the tailbud, FGF signaling in the posterior PSM and the fss gene in the anterior PSM. See text for details. (A-D) The cell-autonomous oscillator: (A) basal dlc expression (asterisk indicates role of DeltaD potentially limited to the tailbud), (B) translation of dlc mRNA to DeltaC protein and activation of Notch signaling feedback to amplify dlc levels, (C) activation of her1 and her7 expression, (D) translation of her1 and her7 mRNA to Her1 and Her7 proteins that repress expression of her1, her7 and dlc. Cycle returns to A and repeats. (E) Intercellular or phase-adjusting function: cell on right in stage C (from above) activates Notch signaling in a neighboring cell (on left) that was previously phase-delayed relative to the right hand cell and phase-advances it from stage A into B by providing exogenous DeltaC.
