Fig. 1. Expression pattern of genes involved in Notch signaling in early gland formation of PV. Transverse serial sections of stage 28, 29 and 30 were analyzed by in situ hybridization. Throughout this paper, all sections that show normal expression patterns are serial and are obtained from the same sample which is staged exactly. Stage 29 PV show the small glands. For stage 30, boxed areas are shown enlarged in the column on the right. (A-C') Expression of chicken SP and epithelial invagination begins at stage 29. At stage 30, chicken SP-negative cells are still observed among luminal cells (arrows). (D-F') Expression of Smad8 is restricted in invaginating epithelium and begins at stage 29. (G-I') Expression of Delta1 in the epithelium begins at stage 29 in a scattered fashion (arrowheads). (J-L',P-R') Expression of Notch1 and Hairy1 is restricted in uninvaginated epithelium. (M-O',S-U') Expression of Notch2 and Hairy2 is strong in invaginated epithelium. (V-X') Numb is homogeneously expressed in the epithelium. Serial sections made from different stage PV and hybridized with the same probe were placed on the same slide glass to compare intensity of signals. Broken lines in K and Q underline borders between epithelium and mesenchyme. Scale bar: 100 µm.