Required for the establishment of the specialized cells of the pituitary gland and the nervous system (By similarity). Involved in the development of interneurons and motor neurons in cooperation with LDB1 and ISL1. Acts as a transcriptional activator. Binds to and activates the promoter of the alpha-glycoprotein gene, and synergistically enhances transcription from the prolactin promoter in cooperation with Pou1f1/Pit-1.