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. Author manuscript; available in PMC: 2014 May 30.
Published in final edited form as: Cell Rep. 2013 Apr 25;3(5):1503–1511. doi: 10.1016/j.celrep.2013.03.036

Figure 7. Model for Axial RA-FGF Antagonism prior to Limb Budding.

Figure 7

Previous genetic studies support FGF8 repression of Meis1/2 in distal limb elements, but our genetic findings show that RA signaling is not required for Meis1/2 expression in the proximal limb. Thus, RA-FGF antagonism is not required along the limb proximodistal axis to provide Meis1/2 expression proximally in the stylopod (blue) and prevent distal expression in the zeugopod (orange) and autopod (green). Instead, our studies support a model in which RA is required earlier for axial antagonization of Fgf8 expression (in both the second heart field and caudal progenitor zone -CPZ) prior to forelimb budding for correct induction and positioning of Tbx5 expression in the forelimb field.

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