The expected and observed expression patterns within the wild type thalamic nuclei are depicted on the left, with the corresponding observed expression pattern for the Arx−/Y mice depicted on the right. Since Dlx2 is upstream of Arx, its expression pattern is unchanged by loss of Arx. In contrast, Six3, Isl-1, and TH, previously demonstrated to require Dlx2 for expression in these areas, are lost upon loss of Arx. This indicates that Arx is also required for their expression, but places it downstream of Dlx2 in the cascade. Gad67 expression is essentially unchanged in the Arx−/Y, indicating that Arx is not required for Gad67 expression in these ventral forebrain regions. Drawings are modified, with permission, from Paxinos et al.’s Atlas of the Developing Mouse Brain at P0 (2007) (45).