NKX2 gene expression in neuroectoderm but not in mesendodermally derived structures depends on sonic hedgehog in mouse embryos

NKX2 genes in vertebrates encode a subfamily of homeodomain-containing transcription factors which regulate morphogenetic events and cell differentiation during embryogenesis. In mouse embryos several NKX2 genes are expressed in the ventral midline domains of the neuroectoderm, while other NKX2 genes are primarily expressed in the mesendoderm and mesendodermally derived organs, such as heart and gut. Within several patterning centers for tissue organization sonic hedgehog (Shh) is an important signal in the formation of ventral midline structures in vertebrate embryos. Here, we investigated the role of Shh in the embryonic expression of six different but closely related NKX2 genes in Shh null mutant mice. We found that expression of NKX2.1, NKX2.2, and NKX2.9 in neural domains requires Shh signaling, whereas NKX2.3, NKX2.5 and NKX2.6 expression in endoderm and mesoderm is independent of Shh.