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. 2006 Nov 24;8(1):104–109. doi: 10.1038/sj.embor.7400867

Figure 1.

Figure 1

Retinoic acid signalling prevents asymmetric Snail1 expression in the anterior presomitic mesoderm. (A–D) Transient asymmetric left–right (L–R) Snail1 expression in the lateral plate mesoderm (LPM) of 4- to 11-somite (som) chicken embryos (Isaac et al, 1997). (E–X) Embryos incubated with PBS, retinoic acid (RA) or disulphiram (DSM) and analysed at the 4-somite (HH8; E–J) or 10-somite stage (HH10; K–X). (Q), (R) and (S) are sections through the LPM at the levels indicated in (L), (N) and (P), respectively. Embryos were hybridized for Snail1 (A–S), Snail2 (T–V) and Lfng (W,X). Exposure to RA abolishes asymmetric L–R Snail1 expression in the LPM (G,H,M,N) without affecting Snail2 expression in the presomitic mesoderm (PSM; T,U). Asymmetric L–R Snail1 expression invades the anterior PSM in HH10 embryos treated with DSM (O,P,S), which delayed segmentation on the side of highest Snail1 expression (X). Asymmetric L–R expression in the LPM is not affected in these embryos (P), where both Snail2 and Lfng continue cycling in the PSM (V–X). Red stars indicate asymmetric L–R expression, red bars the somite boundaries and red arrowheads the newly formed somite boundaries.