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
View: Text | PDF
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

×

Figure 4

Options: View larger image (or click on image) Download as PowerPoint
Lipoatrophy and analysis of BAT gene expression. (a) Representative hist...
Lipoatrophy and analysis of BAT gene expression. (a) Representative histologic appearance of H&E-stained sections from dermal WAT, peri-epididymal WAT, and BAT. For simplicity, only Δ98 mice are shown, but the data are identical in Δ80 mice. (b–d) EM analysis of peri-epididymal WAT precursors in Δ98 mice. The magnifications shown are (b) ×1,900, (c) ×5,000, and (d) ×46,000. Intramitochondrial inclusions of electron-dense material are shown in b and d. The mitochondria are enlarged and show poorly organized cristae. (e and f) EM analysis of BAT precursors in Δ98 mice. Numerous pre-adipocytes adjacent to small capillaries can be seen. Mitochondria are indicated by arrows. The magnifications shown are (e) ×1,900 and (f) ×5,000. P, pre-adipocytes; C, capillaries; L, lipid droplet. (g) Analysis of BAT gene expression. We isolated mRNA from 3-week-old mice and performed real-time RT-PCR with primers encoding the genes indicated at the top of each panel. The data represent means ± SEM of three independent measurements (n = 10 for each genotype). We used amplification of β-actin to normalize gene expression data. Asterisks indicate a statistically significant difference (*P < 0.05 and **P < 0.01 by ANOVA) between genotypes. To measure the levels of immunoreactive Pgc1α, we performed Western blotting with anti-Pgc1α antiserum. We show a representative autoradiogram and a loading control with anti-dynamin antiserum below the Pgc1α real-time PCR graph.