Fig. 2

Flat preparations of 8- to 10- somite-stage embryos injected with notch1a (nic) (B,G), deltaD (C,H) and deltaC (D,I) and deltaD(Pst) RNA (E,K). (A,F) Normal embryos. All embryos have been processed for in situ hybridization with two probes, either MyoD (red) and her1 (blue, A-E) or MyoD (red) and her4 (blue, F-K). Asterisks in B-E and GK label the affected side; arrows point to her1 and her4 domains (blue staining). (B) On the affected side of notch1a-intra (nic) RNA injected embryos, her1 is upregulated within the presomitic mesoderm, but not in the immediate neighbourhood of the somitic territory, and the characteristic her1 stripes cannot be distinguished. Notice that MyoD expression is also unpatterned in the somitic mesoderm. Following nic RNA injection, her4 expression is also upregulated in the presomitic mesoderm on the injected side (notice that there are more blue stained cells on the injected side), MyoD expression in the somitic territory is diffuse (G). Following injection of deltaD (C,H), deltaC (D,I) or deltaD(Pst) RNA (E,K), somitic defects are visible as manifested by the MyoD expression (asterisks). However, her1 and her4 expression are essentially normal. The her1 stripes are clearly separated from each other and the presomitic expression of her4 is as weak as in normal embryos (arrows point to blue cells, compare with F). The diffuse blue colour on the injected side of the embryos in H, I and K is due to activation of her4 transcription in the neural plate (Takke et al., 1999).