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FIG. 2. Xlefty expression during Xenopus development. (A) Whole-mount in situ localization of Xlefty transcripts at gastrula through
tailbud stages. (A) Vegetal pole view, dorsal at top. (B, C, E, J, L, and N) Dorsal view, anterior at left. (D, F, G, K, M, O, P) Left lateral view,
anterior at left. (C, D), (E, F), (I, J), and (M, N) show a dorsal and a left lateral view of the same embryo. Stage of embryo(s) depicted is shown
at the bottom right. (A) During early gastrulation, Xlefty expression predominantly localized to the dorsal blastopore margin. Note the
punctate expression in other regions around the blastopore (arrowheads). (B) As gastrulation proceeded, Xlefty expression became localized
to the prospective floor plate and prechordal plate, but was still present around the closing blastopore (arrowheads). (C, D) During early
neurulation, expression continued to be localized to the prospective floor plate and prechordal plate (arrows), in addition to expression
around the ventrolateral yolk plug (arrowhead). (E, F) As neurulation proceeded, the dorsal midline expression of Xlefty was downregulated
centrally (arrows), resulting in an anterior and posterior domain of expression (arrowheads). (G) Following neurulation, Xlefty expression
appeared in the posterior midline in the floor plate (arrowhead), notochord (asterisk), and hypochord (arrow). (H) The expression in the
floor plate and hypochord remained through tailbud stages (H), while the notochord expression was transient and variable in intensity
(G). The floor plate and hypochord expression progressed in a posterior-to-anterior direction (G) and receded in the opposite direction
(P; data not shown). At st. 23, unilateral Xlefty expression became apparent in the left lateral plate mesoderm (arrowhead in H), then
migrated anteriorly (I), and eventually became localized to the left cardiac field (arrowhead in O). Between st. 24 and st. 25, another
unilateral domain of Xlefty expression emerged in the left anterior dorsal endoderm (arrowheads in K, L) and remained into early tailbud
stages (K). Variable levels of bilateral posterior endoderm expression (arrow in K) were also present from approximately st. 245 through
tailbud stages (K; data not shown). |
