This project studies the regulation of expression of genes encoding lens fiber membrane channel proteins. We are focusing on the regulation of expression of the gene encoding MIP, the major intrinsic protein of the lens fiber membrane, which is specifically expressed in the ocular lens fibers and belongs to an ancient superfamily of transmembrane channel proteins. We characterized 2,840 bp of 5' flanking sequence of the human MIP gene to study the cis regulatory elements responsible for the tissue specificity and developmental regulation of the MIP gene. We found that a DNA fragment containing 253 bp of 5' flanking sequence and 42 bp of exon 1 of the human MIP gene fused to the reporter chloramphenicol acetyltransferase (CAT) gene is able to express the CAT gene in cultured lens cells. We are studying the interaction of transcription factors with the cis regulatory elements of the MIP gene and its effect on the in vitro transcription of the MIP gene in Drosophila nuclear extracts. Purified human Sp1 and Ap2 interact with cis regulatory elements of the MIP promoter and activate the in vitro transcription of the MIP promoter, suggesting its involvement in the regulation of MIP gene transcription. These studies will further our understanding of the role of general transcription factors on the tissue-specific expression of the MIP gene.
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