Trophoblast-Specific Transcription from the Mouse Placental Lactogen-I Gene Promoter

We have isolated the gene encoding mouse placen-tal lactogen-I and characterized the promoter region of this gene by transient and stable transfection. Promoter sequences extending 274 basepairs (bp) up-stream from the start site of transcription contain all of the elements necessary for maximal expres-sion upon transient transfection into the rat chorio-carcinoma Rcho-1 cell line; these Rcho-1 cultures contain both proliferative trophoblast stem cells and terminally differentiated trophoblast giant cells. In stably transfected cell lines, expression from this promoter increases as the percentage of differen-tiated cells in the culture increases. In contrast to these results in trophoblast cells, the 274-bp pro-moter as well as a promoter region extending 2700 bp up-stream of the transcriptional start site are unable to drive transcription in a variety of other cell types. Mutational and protein binding analyses in-dicate that two AP-1 sites are required for maximal expression in Rcho-1 cells, and that the composition of the AP-1 transcription factor may vary as differ-entiation in the cell culture increases. In addition to these two AP-1 sites, at least one other element appears to be critical for promoter activity in tropho-blast cells. (Molecular Endocrinology 7: 181-188, 1993