Fig. 4. Expression of SHH and FGF8 in noggin-infected and control eyes. Embryos were infected at stage 15-18 with RCAS-noggin or RCAS-alkaline phosphatase and were analyzed on E6. (A-F) SHH expression. Both alkaline phosphatase- and noggin-infected eyes expressed SHH very heavily in the ventral neural tube (A,B and D,E), and weakly in the neural retina (arrows, C,F). No apparent changes in either the relative intensity or pattern of distribution of the signals were noted in noggin-infected eyes (D-F) in comparison to controls (A-C). (G-L) PTC expression. Intensity of signals for the transcripts of the SHH receptor patched (PTC) provides an indication of levels of SHH signaling because PTC is upregulated by SHH (Marigo and Tabin, 1996; Goodrich et al., 1996). PTC expression was conspicuous in the neural tube (G; top box enlarged in H); there was very little expression in the neural retina, restricted to the optic nerve head region (G; lower box enlarged in I; arrow points to positive cells). Embryos infected with noggin showed increases in signal in the neural tube (arrows in J; box enlarged in K), likely due to seepage of intravitreally injected virus into the neural tube through the optic stalk. No such increases in PTC signal were observed in the retinae of the same noggin-infected embryos (J, box enlarged in L). (M,N) FGF8 expression. FGF8 was weakly expressed in a region just dorsal to the optic stalk in alkaline phosphatase-infected controls (arrow, M), as well as the optic stalk itself (arrowhead, M). In noggin-infected eyes, however, FGF8 signal was much more intense and found in a larger region than in controls (arrow, N). Scale bars: A,D,G,J,M,N, 500 µm; B,C,E,F,H,I,K,L, 50 µm.
