Fig. 7. Pitx2 functions at multiple developmental stages. Analysis of Pitx2^–/– mice revealed that Pitx2 is required for Rathke’s pouch expansion at early stages of embryogenesis, and studies from Pitx2^neo/neo homozygotes showed that Pitx2 is also required for cell lineage specification at later stages of organogenesis, influencing expression of downstream transcription factors. In addition to Pitx1 function in pituitary hormone transcription, Pitx1 acts synergistically with Pitx2 at an early stage of pituitary development.