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Fig. 1. Six1, FGF8, and Sox3 expression during early Xenopus development. Embryos are shown in dorsal (A, E, I) or lateral (D,H,L) views (anterior to the left). (A) Weak Six1 expression (arrowheads) first appears in dorsoanterior ectoderm at stage 11.5 (A), intensifies at stage 12 (B), and becomes restricted to a crescent (arrowheads) around the anterior neural plate while being downregulated in the anterior neural plate at stage 12.5 (C,D). (E) In addition to circumblastoporal expression, a new domain of FGF8 expression in dorsoanterior ectoderm appears around stage 11.5 (E) and becomes stronger by stage 12 (F). By stage 12.5, expression of FGF8 is downregulated in dorsoanterior ectoderm except for the prospective midbrainindbrain boundary (MHB) and three nested arcs (1) (G,H). (I) Sox3, for comparison, is broadly expressed in dorsal and dorsoanterior ectoderm at stage 11.5 (I) but becomes restricted to the developing neural plate between stage 12 (J) and stage 12.5 (K). At stage 12.5, an additional crescent shaped domain of Sox3 expression (black arrowhead) appears around the anterior neural plate (white arrowhead) (K,L). (M) Sagittal sections through embryo depicted in (G,H) reveal that the two posterior arcs (1,2) of FGF8 expression (M,O) are situated within the anterior neural plate marked by Sox3-immunostaining, whereas the anteriormost arc (3) is located outside of the neural plate. Arrowheads indicate Sox3 immunopositive nuclei immediately rostral to the second arc of FGF8 expression. (P) Schematic summary of FGF8 expression relative to the expression of Sox3, Six1, and other markers based on these data and on our previous report (Schlosser and Ahrens, 2004). Blue line demarcates boundary of the lateral part of the pre-placodal region (LPR) used for grafts and extirpations. Yellow lines indicate boundaries of areas from which ectoderm was taken for anterior neural plate (ANP), posterior neural plate (PNP), lateral neural plate (LNP), and anterior neural ridge (ANR) grafts and extirpations. The green line demarcates the region removed in unilateral extirpations of the entire anterior neural plate (UNP). |
