Expression and regulation of the chicken Nkx-6.2 homeobox gene suggest its possible involvement in the ventral neural patterning and cell fate specification.

Rapid accumulating evidence has suggested that the homeodomain transcription factors of the Nkx family play important roles in controlling vertebrate organ patterning and differentiation. In this study, we report the cloning, expression and regulation of a novel chicken homeobox gene, cNkx-6.2, whose expression is similar, but not identical, to that of mouse Nkx-6.2. The earliest expression of cNkx-6.2 was detected at the neural plate stage in the prospective midbrain and hindbrain regions. As the neural development proceeds, cNkx-6.2 expression was restricted in the ventral region of the entire neural axis except the forebrain region. At late stages of development, cNkx-6.2 expression is downregulated in the ventricular neuroepithelial cells, but subsequently upregulated in a sub-population of cells. Tissue recombination and explant culture experiments demonstrated that expression of cNkx-6.2 can be induced by the notochord signal and purified SHH protein, and repressed by BMP-4 and -7, indicating that the cNkx-6.2 expression can be influenced by both ventral and dorsal midline signals. Taken together, these studies have suggested two different roles for the cNkx-6.2 transcription factor: participating in the Shh-initiated ventral patterning during early CNS development and controlling cell fate specification and differentiation during late development.