Xenbase Image ID: 135478

Figure 6. Molecular relay for heart induction. Inhibitors of canonical Wnt/β-catenin signaling produced by the Organizer act on endoderm to induce Hex, which, in turn, controls the production of a diffusible factor that acts back on mesoderm to induce early cardiac genes (e.g., Nkx2.5 and Tbx5). Hex functions as a transcriptional repressor and might induce production of a diffusible activator by repression of a repressor (shown as ×). Not depicted is the alternate scenario that Hex directly suppresses expression of a diffusible repressor of cardiogenesis. The finding that Hex induced early cardiac markers, whereas Gsk3β and dnTCF3 promoted progression to expression of myocardial markers (MHCα and TnIc), suggests that parallel pathways, perhaps involving activation of JNK and/or PK-C, regulate Hex-independent diffusible factors from the endoderm. Nodal related proteins (XNr) and noncanonical Wnts might complement Hex-dependent heart induction, but it is not yet clear whether they act on endoderm or directly on cardiac mesoderm. Image published in: Foley AC and Mercola M (2005) Copyright © 2005. 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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