SHORT COMMUNICATION The Pit4 Transcription Factor Gene Is a Candidate for the Murine Snell Dwarf Mutation

Two nonallelic mouse mutations with severe dwarf phe-notypes 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-2 and Snell dwarf (dto) genes on mouse chromosome 16. No recombination was observed between Pit-l and dw in 110 individuals examined. Southern blot analysis of genomic DNA reveals that the Pit-l gene is rearranged in C3H/HeJ-d&/dw mice but not in coisogenic +/+ animals, providing molecular evidence that a lesion in the Pit-l gene results in the Snell dwarf phenotype. Dem-onstration of low levels of Pit-l expression in Ames dwarf (df) mice implies that both Pit-l and df expressio