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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

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

We have previously reported the discovery of an islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP) that is predominantly expressed in islet ß-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 ßTC-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 ß-cell-specific gene expression in vivo, it was ligated to a ß-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 ß-galactosidase expression in newborn mouse islets, predominantly in ß-cells, which was initiated during the expected time in development, around embryonic day 12.5. However, unlike the endogenous IGRP gene, ß-galactosidase expression was also detected in the cerebellum. Moreover, ß-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.

Abbreviations: CAT, chloramphenicol acetyltransferase; DTT, dithiothreitol; G6P, glucose-6-phosphate; G6Pase, glucose-6-phosphatase; HNF, hepatocyte nuclear factor-6; IGRP, islet-specific G6Pase catalytic subunit-related protein; PAM, peptidyl-glycine alpha-amidating monooxygenase; PMSF, phenylmethylsulfonyl fluoride; X-gal, 5-bromo-4-chloro-3-indolyl-ß-D-galactopyranoside

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