The Proximal Islet-Specific Glucose-6-Phosphatase Catalytic Subunit–Related Protein Autoantigen Promoter Is Sufficient to Initiate but not Maintain Transgene Expression in Mouse Islets in Vivo

The Proximal Islet-Specific Glucose-6-Phosphatase Catalytic Subunit–Related Protein Autoantigen Promoter Is Sufficient to Initiate but not Maintain Transgene Expression in Mouse Islets in Vivo Claudia Frigeri 1 , Cyrus C. Martin 1 , Christina A. Svitek 1 , James K. Oeser 1 , John C. Hutton 2 , Maureen Gannon 3 and Richard M. O’Brien 1 1 Department of Molecular Physiology and Biophysics, Vanderbilt University Medical School, Nashville, Tennessee 2 Barbara Davis Center for Childhood Diabetes, University of Colorado Health Sciences Center, Denver, Colorado 3 Department of Medicine, Vanderbilt University Medical School, Nashville, Tennessee Address correspondence and reprint requests to Richard M. O’Brien, Department of Molecular Physiology and Biophysics, 761 PRB, Vanderbilt University Medical School, Nashville, TN 37232-0615. E-mail: richard.obrien{at}vanderbilt.edu Abstract We have previously reported the discovery of an islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP) that is predominantly expressed in islet β-cells. IGRP has recently been identified as a major autoantigen in a mouse model of type 1 diabetes. The analysis of IGRP-chloramphenicol acetyltransferase (CAT) fusion gene expression in transiently transfected islet-derived hamster insulinoma tumor and βTC-3 cells revealed that the promoter region located between −306 and +3 confers high-level reporter gene expression. To determine whether this same promoter region is sufficient to confer islet β-cell-specific gene expression in vivo, it was ligated to a β-galactosidase reporter gene, and transgenic mice expressing the resulting fusion gene were generated. In two independent founder lines, this −306 to +3 promoter region was sufficient to drive β-galactosidase expression in newborn mouse islets, predominantly in β-cells, which was initiated during the expected time in development, around embryonic day 12.5. However, unlike the endogenous IGRP gene, β-galactosidase expression was also detected in the cerebellum. Moreover, β-galactosidase expression was almost completely absent in adult mouse islets, suggesting that cis -acting elements elsewhere in the IGRP gene are required for determining appropriate IGRP tissue-specific expression and for the maintenance of IGRP gene expression in adult mice. CAT, chloramphenicol acetyltransferase DTT, dithiothreitol G6P, glucose-6-phosphate G6Pase, glucose-6-phosphatase HNF, hepatocyte nuclear factor-6 IGRP, islet-specific G6Pase cat