Nodal points and complexity of Notch-Ras signal integration

Metazoans utilize a handful of highly conserved signaling pathways to create a signaling backbone that governs all stages of development, by providing spatial and temporal cues that influence gene expression. How these few signals have such a versatile developmental action is of significance to evolution, development, and disease. Their versatility likely depends upon the larger-scale network they form through integration. Such integration is exemplified by cross-talk between the Notch and the Receptor Tyrosine Kinase (RTK) pathways. We examined the transcriptional output of Notch-RTK cross-talk during Drosophila development and present in vivo data that supports a role for selected mutually-regulated genes as potentially important nodal points for signal integration. We find the complex interplay between these pathways involves their mutual regulation of numerous core components of RTK signaling in addition to targets that include components of all the major signalling pathways (TGF-, Hh, Jak/Stat, Nuclear Receptor and Wnt). Interestingly, Notch-RTK integration did not lead to general antagonism of either pathway, as is commonly believed. Instead, integration had a combinatorial effect on specific cross-regulated targets, which unexpectedly included the majority of Ras-responsive genes, suggesting Notch can specify the response to Ras activation.

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Hurlbut GD, Kankel MW, Artavanis-Tsakonas S