The Pit-1 transcription factor gene is a candidate for the murine Snell dwarf mutation

Two nonallelic mouse mutations with severe dwarf phenotypes are characterized by a lack of growth hormone, prolactin, and thyroid stimulating hormone. The cells that normally synthesize these pituitary hormones express a common transcription factor called GHF-1 or Pit-1. Using an intersubspecific backcross, we have demonstrated tight linkage of the Pit-1 and Snell dwarf (dw) genes on mouse chromosome 16. No recombination was observed between Pit-1 and dw in 110 individuals examined. Southern blot analysis of genomic DNA reveals that the Pit-1 gene is rearranged in C3H/HeJ-dwJ/dw mice but not in coisogenic +/+ animals, providing molecular evidence that a lesion in the Pit-1 gene results in the Snell dwarf phenotype. Demonstration of low levels of Pit-1 expression in Ames dwarf (df) mice implies that both Pit-1 and df expression may be required for pituitary differentiation.