Fig. 2. Comparison of the Sox10, Mitf and Bmp expression patterns during the initial stages of chick eye development. (A) Schematic illustrating the location of the section in H, showing the nasal part of the optic vesicle at stage 10/11. (B) Bmp4 expression in the surface ectoderm overlying the optic vesicle following whole-mount in situ hybridisation (13 somites). The optic primordium is shown at stage 8 (6 somites; C,F,I,L,O), at stage 9 (7-9 somites; D,G,J,M,P) and stage 10 (10-12 somites; E,H,K,N,Q). (C) At stage 8, Sox10-positive neural crest cells are observed in the dorsal neural folds of the prosencephalon (arrows). (D) Sox10-expressing neural crest cells are detected in the dorsal-most region of the prosencephalon (arrows) and no transcripts are detected distally. (E) Sox10 expression is detected in neural crest cells overlying the dorsal part of the optic vesicle (arrows). (F) At stage 8, Mitf expression is not observed in the optic primordium (arrow). (G) Mitf expression is strongest in the distal part of the optic vesicle at stage 9 (arrows). The arrowheads indicate neural crest cells dorsally. (H) At stage 10, Mitf expression is observed in the presumptive RPE (dorsal optic vesicle) and in the distal part (arrows). See A for the location of this section; see also R,S,T. (I) Bmp7 expression is observed in the ectoderm overlying the optic primordium at stage 8 (arrows), and diffuse expression is detected in the neural folds (arrowheads). (J) Parallel section of the embryo shown in G. At stage 9, strong Bmp7 expression is observed in the overlying ectoderm (arrows). Bmp7 transcripts are also detected in the dorsal ectoderm that covers the neural crest cells (arrowheads). (K) Bmp7 expression in the ectoderm overlying the distal region of the optic vesicle at stage 10 (arrows). Transcripts are still observed in the ectoderm overlying the mesenchyme (arrowhead). (L) At stage 8, Bmp4 transcripts are detected in the overlying ectoderm (arrow) and in the neural folds (arrowheads). (M) Strong Bmp4 expression is detected in the ectoderm overlying the distal portion of the optic vesicle at stage 9 (arrows). Weak or no expression is observed in the dorsal-most ectoderm overlying the mesenchymal cells (arrowheads). (N) At stage 10, Bmp4 expression is still strong in the ectoderm overlying the distal portion of the optic vesicle (arrows), whereas weak expression is observed in the ectoderm overlying the surrounding mesenchyme (arrowhead). Note that Bmp4 expression appears to be stronger in the ectoderm overlying the dorsal portion of the optic vesicle. (O) At stage 8, Bmp5 expression is strong in the dorsal midline, the neural folds (arrowheads). Transcripts appear to be absent from the overlying ectoderm. (P) Bmp5 expression weakens in the dorsal midline at stage 9 (arrowhead). (Q) No Bmp5 transcripts are detected in the neuroepithelium of the chick optic vesicle and surrounding tissues (arrow) at stage 10. (R) Nasal region of the optic vesicle at stage 10. Mitf expression in the distal and dorsal part of the optic vesicle (arrowheads). (S) Higher magnification of the Mitf expression pattern in the more-temporal region of the optic vesicle shown in H. Mitf expression is detected in both the dorsal and distal region of the optic vesicle (arrowheads), although expression weakens ventrally (arrow). (T) In the most-temporal region of the optic vesicle, Mitf expression is downregulated in the disto-ventral region (arrow).