September 1, 2000;
Developmental expression of the Xenopus Nkx2-1 and Nkx2-4 genes.
The homeodomain transcription factor Nkx2-1 (TTF-1) plays an essential role in the development of the thyroid
and ventral forebrain
. We report the cloning and developmental expression patterns of two Xenopus NK-2 genes, Nkx2-1 and Nkx2-4, that are closely related to Nkx2-1. These genes show readily distinguishable expression patterns during development. Similar to its orthologues in chicken and mouse, the Xenopus Nkx2-1 gene is expressed in the developing thyroid
, and ventral forebrain
. In contrast, expression of Nkx2-4 is specifically localized to the ventral diencephalon
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Fig. 2. Developmental expression of Xenopus Nkx2-1 and Nkx2-4. (A–I,P,Q) whole-mount in situ hybridizations, and (K–O) transverse sections. (A–C) Lateral view of stage 23, 32 and 37 embryos, respectively, expressing Nkx2-1. The narrow arrow represents diencephalon expression, the wide arrow shows the telencephalon, the open arrowhead indicates the thyroid anlage and the closed arrowhead indicates lung primordia. (D–F) Lateral views of stage 22, 32 and 37 embryos, respectively, showing expression of Nkx2-4 exclusively in the ventral diencephalon. (G) Dorsal view of stage 32 embryo showing Nkx2-1 expression in the telencephalon (arrowhead) and diencephalon (arrow). (H) Dorsal view of a stage 32 embryo showing Nkx2-4 expression in the diencephalon (arrow). (I) Double in situ hybridization analysis. Dorsal view of stage 34 embryo showing overlapping Nkx2-1 and Nkx2-4 expression in the diencephalon (purple-blue) indicated by arrow, and Nkx2-1 expression in the forebrain (pink) indicated by the arrowhead. (K–O) Transverse sections photographed at 200×. The planes of the respective sections are indicated (J). (K) Section through the forebrain of a stage 32 embryo showing Nkx2-1 expression in the ventral telencephalon. (L) Nkx2-1 and (M) Nkx2-4 expression in the ventral diencephalon of stage 32 embryos. (N) Nkx2-1 expression in the thyroid anlage of a stage 35 embryo (arrow). (O) Nkx2-1 expression in the developing lung anlage of the same stage 35 embryo (arrow). (P) Ventral view of a stage 39 embryo showing Nkx2-1 expression in the lung buds (arrows). (Q) In situ hybridization of entire isolated gut tissues from a stage 45 embryo showing Nkx2-1 expression in the distal tips of the developing lungs. e, eye; de, diencephalon; h, heart; nt, neural tube; te, telencephalon.