Liver-specific expression of the mouse alpha-fetoprotein gene is mediated by cis-acting DNA elements.

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Abstract
We have identified cis-acting regulatory elements in the 5'' flanking region of the mouse .alpha.-fetoprotein (Afp) gene, using the expression of the bacterial gene for chloramphenicol acetyltranferase (CAT) in a transient expression assay. Tissue-specific enhancer activity was determined by transfection of mouse hepatoma (BWTG3) and fibroblasts cells (C127, NIH 3T3) with various DNA fragments linked to the CAT gene. A 5,4-kilobase restriction fragment was shown to have characteristics typical of enhancers, including the ability to function independent of orientation and position and the ability to enhance transcription from a heterologous promoter. The enhancer activity was greatest in the hepatoma cells, which express Afp. By deletion analysis, it was demonstrated that enhancer activity is present in several subfragments, indicating the presence of more than one element in this fragment. An additional regulatory element within 950 base pairs of the Afp transcription initiation site has been identified and shown to confer tissue-specific expression on the CAT gene. This fragment, which lacks enhancer activity, contains the Apf promoter region and mediates the tissue-specific expression of the CAT gene when driven by nonspecific viral enhancers. We conclude from our studies that there are several types of regulatory elements in the 5'' flanking region of the Afp gene that help mediate tissue-specific expression.