Fig. 3. The expression profile of proneural bHLH genes is altered in the Notch1^- retina. To visualize the domain of -Cre-mediated recombination, AP activity was monitored on sections from E13.5 -Cre;Z/AP control (A) and Notch1^f/f;-Cre;Z/AP mutants (H). The black arrowheads indicate the peripheral retina where Cre activity is detected. The expression of Hes5 (B,I), Neurod1 (C,J), Ngn2 (D,K), Mash1 (E,L), Math5 (F,M) and Math3 (G,N) were determined by in situ hybridization. In control eyes (B-G), the normal pattern of bHLH gene expression was observed, while a change in the expression profile of these factors was detected in the Notch1^f/f;-Cre;Z/AP eyes (I-N). The expression of Hes5 was reduced (compare I with B), the expression of Neurod1, Ngn2, Math5 and Math3 was enhanced (compare J,K,M,N with C,D,F,G), and the expression of Mash1 appears unchanged (compare L with E) in the Notch1^f/f;-Cre;Z/AP when compared with -Cre;Z/AP controls. le, lens; oc, optic cup. Scale bar: 100 µm.