Demarcation of ventral territories by the homeobox gene NKX2.1 during early chick development.

Members of the NK-2 homeobox gene family are expressed in distinct parts of the central nervous system and in other non-neural territories not only in the fruitfly Drosophila melanogaster, but also in vertebrates. The murine Nkx2.1 (TTF-1, T/ebp) gene was previously shown to be active and indispensable in the developing forebrain, hypophysis, thyroid and lung. Here we report the early transcript distribution of the chick NKX2.1 gene. By whole-mount in situ hybridization we detect a novel transient expression domain in the early epiblast. Further expression occurs in the ventral medial endoderm, which becomes restricted to the anlage fields of the thyroid and lung, in the ventral diencephalon and telencephalon. These findings suggest that NKX2.1 is part of a Nkx code which specifies ventral territories in the vertebrate embryo.