Mosaic analysis of insulin receptor function
Tadahiro Kitamura, Yukari Kitamura, Jun Nakae, Antonio Giordano, Saverio Cinti, C. Ronald Kahn, Argiris Efstratiadis, Domenico Accili
Tadahiro Kitamura, Yukari Kitamura, Jun Nakae, Antonio Giordano, Saverio Cinti, C. Ronald Kahn, Argiris Efstratiadis, Domenico Accili
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Article Endocrinology

Mosaic analysis of insulin receptor function

Abstract

Insulin promotes both metabolism and growth. However, it is unclear whether insulin-dependent growth is merely a result of its metabolic actions. Targeted ablation of insulin receptor (Insr) has not clarified this issue, because of early postnatal lethality. To examine this question, we generated mice with variable cellular mosaicism for null Insr alleles. Insr ablation in approximately 80% of cells caused extreme growth retardation, lipoatrophy, and hypoglycemia, a clinical constellation that resembles the human syndrome of leprechaunism. Insr ablation in 98% of cells, while resulting in similar growth retardation and lipoatrophy, caused diabetes without β-cell hyperplasia. The growth retardation was associated with a greater than 60-fold increase in the expression of hepatic insulin-like growth factor binding protein-1. These findings indicate that insulin regulates growth independently of metabolism and that the number of insulin receptors is an important determinant of the specificity of insulin action.

Authors

Tadahiro Kitamura, Yukari Kitamura, Jun Nakae, Antonio Giordano, Saverio Cinti, C. Ronald Kahn, Argiris Efstratiadis, Domenico Accili

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Evaluation of Insr mosaicism. (a) RT-PCR analysis. We isolated mRNA from...
Evaluation of Insr mosaicism. (a) RT-PCR analysis. We isolated mRNA from liver of individual mosaic (lanes 1–6) and WT (lane 7) mice. Because of the deletion of Insr exon 4, the length of the PCR product generated from the ΔloxP allele is smaller (350 bp) than the WT allele (500 bp) (upper panel). (b) Protein levels of Insr and Igf1r were examined by Western blotting as indicated in Methods. The first and second panels from the top show different exposures of the same autoradiogram to better visualize Insr expression in mice with greater degrees of mosaicism. The third panel from the top shows samples from the same set of mice analyzed with anti-Igf1r antiserum to normalize protein levels. (c) Expression level of Insr in various tissues in Δ80 and Δ98 mice by Western blotting. We removed brain, liver, skeletal muscle, and BAT and determined protein levels of Insr and Igf1r by Western blotting as indicated in Methods.