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Fig. 8. Changes in placodal gene expression patterns during neurulation in Xenopus embryos (stages 16–18). As in Fig. 1, color-coded arrows and arrowheads are used for the identification of comparable regions of gene expression indicated in the schematic drawing. Green arrowhead indicates the prospective olfactory placode. The green asterisk indicates an anterior subregion of the lateral Pax6-expressing domain, where panplacodal genes such as Eya1 and Six1 are downregulated during neurulation (note indentation in the red domain) and which will likely give rise to the lens placode. Green arrow indicates the posterior subregion of the lateral Pax6-expressing domain (prospective trigeminal placode). (A and B) Sagittal sections through the anterior neural folds reveal expression of Six1 (A) and Sox3 (B) in the deep ectodermal layer of the outer neural folds (black arrows). The outer ectodermal layer is indicated by black asterisks. (C–E) Frontal views of gene expression domains in neural fold stage Xenopus embryos. Note the separation of the anterior domain of Eya1 and Six1 expression (arrowheads) from the lateral domain (arrows) due to the elevation of the neural folds. (F–H) Lateral views of gene expression domains in neural fold stage Xenopus embryos. Note the downregulation of Eya1 (F), Six1 (G), and Msx1 (H) in a region that will likely give rise to the lens placode (green asterisk). The white asterisk in H indicates expression of Msx1 in a region encompassing neural crest and lateralmost neural plate. For detailed description, see text. Abbreviations: cg, cement gland; nep, anterior neuropore. For additional abbreviations, see Fig. 1. |
