Teratogenic doses (1 μM), but not 20 nM, RA alter the expression of early markers of anterioposterior axis specification. (A-F) In comparison to controls, expression of the anterior neural plate markers six3a (A-C) and otx2 (D-F) is unaffected by 20 nM RA but is completely abolished in the presence of a teratogenic dose. (G-L) By contrast, expression of the posterior neural plate markers hoxb1b (G-I) and gbx1 (J-L) is greatly expanded in embryos treated with a teratogenic dose of RA, whereas embryos treated with 20 nM RA show only a mild or no anterior expansion in comparison to control embryos. Scale bar: 90 μm.
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