IGF-I transcript levels in whole-liver tissue, in freshly isolated hepatocytes, and in cultured hepatocytes from lean and obese Zucker rats.

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Abstract

The mechanisms underlying the maintenance of normal to high rates of linear growth and plasma insulin-like growth factor I (IGF-I) levels in spite of a low growth hormone secretion in obese children remain unknown. Among the animal models of early-onset obesity, obese Zucker (FA/FA) rats (which are homozygous for an inactivating missense mutation in the leptin receptor) are particularly appropriate, because their linear growth shows this growth hormone independence.

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Single-step method of RNA isolation by acid guanidinium thiocyanate-phenol-chloroform extraction.

P. Chomczynski, N Sacchi (1987)

A new method of total RNA isolation by a single extraction with an acid guanidinium thiocyanate-phenol-chloroform mixture is described. The method provides a pure preparation of undegraded RNA in high yield and can be completed within 4 h. It is particularly useful for processing large numbers of samples and for isolation of RNA from minute quantities of cells or tissue samples.

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Identification and expression cloning of a leptin receptor, OB-R.

Louis A Tartaglia, Marlene Dembski, Xun Weng … (1995)

The ob gene product, leptin, is an important circulating signal for the regulation of body weight. To identify high affinity leptin-binding sites, we generated a series of leptin-alkaline phosphatase (AP) fusion proteins as well as [125I]leptin. After a binding survey of cell lines and tissues, we identified leptin-binding sites in the mouse choroid plexus. A cDNA expression library was prepared from mouse choroid plexus and screened with a leptin-AP fusion protein to identify a leptin receptor (OB-R). OB-R is a single membrane-spanning receptor most related to the gp130 signal-transducing component of the IL-6 receptor, the G-CSF receptor, and the LIF receptor. OB-R mRNA is expressed not only in choroid plexus, but also in several other tissues, including hypothalamus. Genetic mapping of the gene encoding OB-R shows that it is within the 5.1 cM interval of mouse chromosome 4 that contains the db locus.

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Modulation of insulin activities by leptin.

D. Novick, Sidney Rubinstein, Justus B. Cohen (1996)

Leptin mediates its effects on food intake through the hypothalamic form of its receptor OB-R. Variants of OB-R are found in other tissues, but their function is unknown. Here, an OB-R variant was found in human hepatic cells. Exposure of these cells to leptin, at concentrations comparable with those present in obese individuals, caused attenuation of several insulin-induced activities, including tyrosine phosphorylation of the insulin receptor substrate-1 (IRS-1), association of the adapter molecule growth factor receptor-bound protein 2 with IRS-1, and down-regulation of gluconeogenesis. In contrast, leptin increased the activity of IRS-1-associated phosphatidylinositol 3-kinase. These in vitro studies raise the possibility that leptin modulates insulin activities in obese individuals.