Fig. 6. Control (A,C,E,G,I,K) or her6MO-injected (B,D,F,H,J,L) embryos probed for the expression of the Notch pathway genes notch1a/des (A-D), lfng (E,F), notch6 (G,H), notch5 (I,J) and notch1b (K,L) at 14- to 18 ss. Staining was developed for exactly the same amount of time on control MO- and her6MO-injected embryos, to allow for a precise comparison of the gene expression levels. Levels of notch1a/des expression are high in the posterior PSM, decrease towards the anterior PSM and become very low in the somites (A,C). The transition between PSM and somites is defined by a sharp drop in notch1a/des expression. In 6 ng her6MO-injected embryos (B,D), this downregulation is impaired and expression of notch1a/des persists in the newly formed somites. No abnormalities are observed in the expression pattern of notch1b, notch5, notch6 (H,J,L). Expression of lfng is upregulated, but not disrupted, in the neural tube and newly formed somites (F).