Xenbase Image ID: 135674

Model for Xenopus vertebrate segmentation. Segmental regulation of Notch pathway genes in the paraxial mesoderm ofXenopus embryos. The presomitic mesoderm of Xenopusembryos can be divided into three regions, TBD (red shading), TZ (blue shading), and somitomeric region (green shading) in which the Notch pathway is regulated by different factors. The Notch pathway is active when paraxial cells are in the TBD but is repressed in posterior half- segments when cells enter the TZ. This repression is likely to be due to several factors including negative feedback via ESR-5, as well as segmental repressors such as the Hairy-oscillator. At this point in the process, Notch signaling acts to establish segment size by restricting the domain in which the Notch pathway genes are active. In the somitomeric region, Notch signaling appears to take on another role in which ESR-5 appears to promote the expression of Thylacine1and X-Delta-2 in a positive feedback loop. Positive feedback would act to maintain segmental identity by preserving the domains in which Notch signaling occurs. Image published in: Jen WC et al. (1999) Copyright © 1999. Image reproduced on with permission of the Publisher, Cold Spring Harbor Laboratory Press. This is an Open Access article. Larger Image Printer Friendly View

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