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FIG. 3. Sections showing expression of Xbr-1, BMP-4, and X-Notch-1 during eye development, after whole-mount in situ hybridization. (A, B, C, D, E, H, K) Expression of Xbr-1 (I, L), expression of X-Notch-1 (G, J), and expression of BMP-4. (A, B, C) Transverse sections at the levels of the eyes at stage 25 (A), stage 26 (B), and stage 278 (C). Expression is found in the area between the prospective neural retina and the pigment epithelium (A) and ends up in the margin of the eye (C). Note that the pigment epithelium thins out during development (from A to C) and eventually envelops the back of the neural retina (arrows in J, K, L). (D) Posterior transverse section of a stage 25 embryo showing expression of Xbr-1 in the dorsal neural tube (dt) and the lateral mesoderm (lm). (E, F) Comparison of Xbr-1 and X-Notch-1 expression in the eyes at stage 25/26. The area between arrowheads expresses Xbr-1 (E) but not X-Notch-1 (G). Note that at this stage X-Notch-1 is expressed uniformly in the prospective neural retina. (G, H, I, J, K, L) High magnification of sections through the eyes, showing a comparison between expression of BMP-4 (G, J), Xbr-1 (H, K), and X-Notch-1 (I, L) at stage 31/32 (G, H, I) and stage 33/34 (J, K, L). The area of the eye that expresses Xbr-1 (H, K) and BMP-4 (G, J) is the part of the prospective dorsal ciliary margin and is included between arrowheads. These sections show that expression of BMP-4 and Xbr-1 in the eye is largely coincident at both stages. The same area of the eye appears negative for X-Notch-1 expression (area between arrowheads in I, L). Note that as the neural retina differentiates, between stages 312 (I) and 33/34 (L), X-Notch-1 expression becomes gradually restricted to the periphery of the eye, but is never observed at the very edge of the eye (arrowheads). In (G, H, I) the prospective pigment epithelium has thinned out and cannot be easily distinguished. In (J, K, L) arrows point to the pigment epithelium which is now easily recognizable by the brown pigment. In some sections the lens (l) has been detached. Abbreviations: di, diencephalon; dt, dorsal neural tube; l, lens; lm, lateral mesoderm; n, notochord; nr, prospective neural retina; pe, prospective pigment epithelium; s, somite. |
