LOCAL EXPRESSION OF A POU FAMILY TRANSCRIPTION FACTOR, PIT-1, IN THE RAT PLACENTA

A pituitary-specific trans-acting factor, Pit-1 regulates transcriptio nal activity of growth hormone (GH) and prolactin (PRL) genes. Pit-1 c an bind and activate the promoters of human chorionic somatomammotropi n (hCS-A) and placental GH variants (hGH-V) as well. However, expressi on of Pit-1 in the rat placenta has nor yet been elucidated. The prese nt study aims to determine whether the Pit-1 gene is locally expressed in the rat placenta using reverse transcription-polymerase chain reac tion (RT-PCR), Northern blot and Western blot hybridization, in situ h ybridization and immunohistochemistry. PCR products were further analy zed by Southern hybridization and DNA sequencing. The estimated size o f Pit-1 mRNA in placenta was very similar to that in anterior pituitar y (AP). PCR products from placenta were exactly the same size with tha t from AP and confirmed as Pit-1-specific by Southern hybridization. T he Pit-1 specific sequence was also confirmed by sequencing of partial amplification fragments. Immunoreactive 33 kDa Pit-1 was present in t he placenta as well as in AP. Pit-1 specific mRNA and protein were loc alized in the trophoblast cells of placenta. These data suggest that P it-1 is locally synthesized in the rat placenta and may be involved in the regulation of GH- and/or PRL-like gene expression in the placenta .