Diabetes 50:63-68, 2001
© 2001 by the American Diabetes Association, Inc.
A Genetic Defect in ß-Cell Gene Expression Segregates Independently From the fa Locus in the ZDF Rat
Steven C. Griffen,
Juehu Wang, and
Michael S. German
From the Hormone Research Institute (S.C.G., J.W., M.S.G) and the
Department of Medicine (S.C.G., M.S.G.), University of California, San
Francisco, California.
Address correspondence and reprint requests to Michael S. German, MD, HSW
1090, Box 0534, 513 Parnassus Ave., San Francisco, CA 94143. E-mail:
mgerman{at}biochem.ucsf.edu
.
Type 2 diabetes is a strongly genetic disorder resulting from inadequate
compensatory insulin secretion in the face of insulin resistance. The Zucker
diabetic fatty (ZDF) rat is a model of type 2 diabetes and, like the human
disease, has both insulin resistance (from a mutant leptin receptor causing
obesity) and inadequate ß-cell compensation. To test for an independently
inherited ß-cell defect, we examined ß-cell function in fetuses of
ZDF-lean rats, which have wild-type leptin receptors. ß-Cell number and
insulin content do not differ among wild-type, heterozygous, and homozygous
ZDF-lean fetuses. However, insulin promoter activity is reduced 30-50% in
homozygous ZDF-lean fetal islets, and insulin mRNA levels are similarly
reduced by 45%. This is not a generalized defect in gene expression nor an
altered transfection efficiency, because the islet amyloid polypeptide
promoter and viral promoters are unaffected. Insulin promoter mapping studies
suggest that the defect involves the critical A2-C1-E1 region. This study
demonstrates that the ZDF rat carries a genetic defect in ß-cell
transcription that is inherited independently from the leptin receptor
mutation and insulin resistance. The genetic reduction in ß-cell gene
transcription in homozygous animals likely contributes to the development of
diabetes in the setting of insulin resistance.

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Copyright © 2001 by the American Diabetes Association.
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