This project studies the regulation of expression of genes encoding lens fiber membrane channel proteins, which are essential for maintaining the transparency and correct refractive index of the lens. We are presently focusing on the regulation of expression of the gene encoding MIP, the major intrinsic protein of the lens fiber membrane, that is specifically expressed in the ocular lens fibers and belongs to an ancient family of transmembrane channel proteins. The characterization of regulatory elements involved in the regulation of the MIP gene promoter led us to the study of transcription factors expressed in the lens. We found that the transcription factor AP2 alpha is expressed in the lens epithelia but not in the lens fibers. We have characterized a novel alternative spliced variant of the AP2 alpha gene expressed in the lens, which lacks part of the activation domain. The presence of several AP2 alpha gene variants functioning as activators or repressors in different compartments of the lens has implications for understanding the spatial regulation of gene expression in the lens. Present studies focus on the interaction of the activator and repressor isoforms of the transcription factor AP2 alpha with other proteins expressed in the lens. Several members of the Sp family of transcription factors are expressed in the lens. Studying their spatial localization in the lens and their interaction with other nuclear proteins, will provide new insights into understanding their role in gene expression and regulation of cell cycle during lens differentiation. In collaboration with Drs. Dwight Stambolian (University of Pennsylvania) and Jack Favor (GSF-Institut fuer Saugetiergenetik, Germany) we have characterized at the molecular level the Hfi mouse genetic cataract, which localizes to the MIP gene locus. We found that a deletion in the exon2/intron3 junction of the MIP gene results in deletion of exon 2 in the resultant transcript, produced by a mechanism involving exon skipping.
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