Fig. 4. Initiation of Notch signal oscillation correlates with the onset of Mesp2 transcription. (A-I) Sections of early stage mouse embryos (E7.0) were analyzed by double immunostaining. (A-C) The embryos were stained with DAPI (A), and with antibodies against NICD and Tbx6 (B,C). A higher magnification image of B is shown in C. These embryos showed weak NICD activity without oscillation, and Tbx6 expression (n=13). (D-I) Sections were also subjected to double staining for Hes7 mRNA and NICD (D-F), and Lfng mRNA and NICD (G-I). Hes7 and Lfng mRNAs were weakly expressed, but did not show clear wave-like patterns (n=10). (J-N) Sections of late-streak stage embryos just prior to somite formation (E7.5) were stained with DAPI to show the embryonic structure (J), and double stained for Tbx6 and Mesp2 (K,L), or Mesp2 and NICD (M,N). Higher magnification images for K and M are shown in L and N, respectively. An oscillatory pattern of Notch activity was detected and the spatial patterns of the three factors were similar to those of later stage embryos (n=12). Ex, extraembryonic region; Emb, embryonic region.