Pit-1 is a pituitary-specific transcription factor responsible for pituitary development and hormone expression in mammals. Pit-1 is important for the activation of the growth hormone and prolactin genes and for the hormonal regulation of the prolactin and thyrotropin-beta subunit genes. Mutation of the Pit-1 gene have been found in dwarf mouse strains displaying hypoplasia of growth hormone, prolactin, and thyrotropin-beta subunit through various molecular mechanisms.