Fig. 8. An autoregulatory feedback loop controls dosage dependent Nodal signals responsible for embryonic patterning. Nodal null embryos fail to induce an AVE at 5.5dpc. Cripto-null, and some Nodal^600/– and Foxh1^–/– embryos induce but fail to rotate the AVE at 6.0 dpc, owing to lowered Nodal signaling. Other Nodal^600/–, and Foxh1^–/– embryos rotate the AVE but fail to induce the ADE at 6.5 dpc, resulting in reduction of the forebrain at 8.5 dpc. Nodal^600/600 embryos have yet higher level of Nodal signaling and correctly induce and rotate the AVE and induce the ADE at 6.5 dpc, yet they fail to establish the LR axis correctly at 8.5 dpc, resulting in defects in heart looping visible at 9.5 dpc.

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