Nkx2.9 Contributes to Mid-Hindbrain Patterning by Regulation of mdDA Neuronal Cell-Fate and Repression of a Hindbrain-Specific Cell-Fate

is a member of the NK homeobox family and resembles both in homology and expression pattern. However, while is required for development of serotonergic neurons, the role of in the mid-hindbrain region is still ill-defined. We have previously shown that expression is downregulated upon loss of during development. Here, we determined whether mdDA neurons require during their development. We show that is strongly expressed in the IsO and in the VZ and SVZ of the embryonic midbrain, and the majority of mdDA neurons expressed during their development. Although the expression of and are slightly affected during development, the overall development and cytoarchitecture of TH-expressing neurons is not affected in the adult -depleted midbrain. Transcriptome analysis at E14.5 indicated that genes involved in mid- and hindbrain development are affected by -ablation, such as and . Although the expression of extends more rostral into the isthmic area in the mutants, the establishment of the IsO is not affected. Taken together, these data point to a minor role for in mid-hindbrain patterning by repressing a hindbrain-specific cell-fate in the IsO and by subtle regulation of mdDA neuronal subset specification.