| Abstrakt: |
In tissue development, juxtacrine signaling often propagates across cells, carrying and delivering temporal and spatial information for cells to make correct patterning. Observed complex and accurate tissue patterning indicates that signaling propagation via ligand-receptor interactions is precisely controlled. It is important and interesting to reveal the possible control mechanisms. The directionality of signaling in cells, which is a common issue for all intercellular signaling pathways, is a critical aspect. To understand the propagation of Notch signaling in presomitic mesoderm cells in the mouse, a novel method is used to build a multicellular model to simulate Notch signaling. Simulation reveals that the transient block of Notch by Notch induced Lfng and the delayed removal of the block by another Notch induced protein Hes7 may explain the observed unidirectional propagation of Notch signaling in these cells. Both mutation in and overexpression of lfng cause the same signaling profile in the tissue, due to the inappropriate timing of Notch signaling block by Lfng. The reverse Notch/Delta signaling quickly develops into reciprocating signaling among cells, causing irregular expression of cyclic genes. Irregular Notch signaling in cells would change their response to the positional information provided by the Fgf8 gradient, resulting in disordered and irregular somite segmentation. As Notch signaling is highly conserved, we hypothesize that the mechanism of controlling unidirectional propagation of signaling in cells by transient receptor block may exist in other tissues and in other vertebrates. Our simulation results also suggest that segmentation clock and unidirectional propagation may be inherently coupled in Notch signaling [ABSTRACT FROM PUBLISHER] |
