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Fig. 5. Positioning of gene expression domains at the anterior neural plate border as revealed by double-staining procedures in sagittal sections (anterior is to the left) of neural plate stage Xenopus embryos (stages 13–14). For each gene analyzed, a first panel depicts gene expression at the anterior neural plate border, a second panel shows the pattern of nuclear Sox3 immunostaining in the same section (apparent nonnuclear staining in the endoderm is an artifact due to autofluorescence of yolk granules), and a third panel presents a superposition of the first two panels. (A–C) Distribution of Sox3 expression (A) and Sox3 immunostaining (B). The anterior border of the neural plate is indicated by grey arrows. The superficial ectodermal layer is indicated by asterisks. Sox3 expression and immunostaining is found in the superficial (in the domain marked by a white asterisk) and deep ectodermal layers. The rostral limit of expression in the deep ectodermal layer (black arrowheads) extends beyond the neural plate border. Cells within this area of Sox3 expression rostral to the neural plate border are also immunopositive for Sox3 (black arrows). However, no Sox3-immunopositive cells are yet discernible in the lateral crescent-shaped domain of Sox3 expression (identified by blue arrowheads in A) as is particularly evident in the inserts of A–C depicting sections of the same specimen at a more lateral level. (D–R) Comparison of the expression pattern of Six1 (D–F), Eya1 (G–I), Dlx3 (J–L), Msx1 (M–O), and Pax6 (P–R) at the anterior neural plate border with Sox3 immunostaining. Inserts in D and G show Six1 and Eya1 expression patterns, respectively, in additional specimens. The borders of expression of each gene in the deep ectodermal layer are indicated by arrowheads. Double-labeled cells, which show expression of the respective gene as well as Sox3 immunostaining, are identified by black or white arrows. Because Pax6 expression and Sox3 immunoreactivity are largely coextensive, double-labeled cells are not specifically marked in P–R. Black asterisks indicate the superficial ectodermal layer (which is artifactually missing in D). White asterisks in L indicate cells in the superficial ectodermal layer that express Dlx3 and are Sox3 immunopositive (posterior border ofDlx3 expression is immediately to the right of panel). Red arrows in M–O indicate Sox3-immunopositive cells located rostral to the domain of Msx1 expression in the anteriormost neural plate. Scale bar in A: 100 μm (for all panels). |
