Figure 3.

Delayed or accelerated somite formation provoked by Snail2 overexpression or dominant–negative Snail2 expression in the chick. Chicken embryos electroporated with pCX-dEGFP plus pCX (A–E), pCX-Snail2 (F–J) or a dominant-negative form of Snail2 (pCX-ΔZf-Snail2; K–O) showing dEGFP expression (A,F,K), their morphology (B,G,L) and the expression of Lfng (C,H,M), Hairy2 (D,I,N) and EphA4 (E,J,O). High levels of ectopic expression were observed in the right presomitic mesoderm (PSM) of the embryos. Brackets indicate the progress of PSM expression. The asymmetric phase of the cycling genes represented in this figure corresponds to embryos in which the differences were more apparent. Red bars indicate somite boundaries, red arrowheads the newly formed boundaries and black arrowheads indicate an extra band of EphA4 expression.