Hypothesize a mechanism to explain how tissues respond to insulin in different ways, even tissues that have the same amount of the receptor.

Insulin is a protein hormone secreted by the β-cells of islets of Langerhans in the pancreas. It has an important effect on the metabolism of carbohydrates, lipids and proteins by promoting the absorption of glucose present in the blood by fat cells, liver cells and those of skeletal muscles.

Insulins reduce blood sugar by a double action:

- by stimulating the peripheral uptake of glucose, in particular by skeletal muscle (by promoting the synthesis of glucogen) and adipose tissue (by promoting the synthesis of lipids).

- by inhibiting the hepatic production of glucose. This shows that the action of insulin on the hepatocytes is different from that of other cells.

To explain these differences, we must address notions of genetics, and more specifically epigenetics: All these cells have the same genome (identical DNA), but the expression of the latter in the different cells are very different. For example, for adipocytes, the expression of the enzymes involved in lipogenesis is favored, whereas the expression of the enzymes of glucogenogenesis is favored in the muscle cells, and in the liver there is a genetic overexpression of the enzymes of neoglucogenesis.

this protocol provides a detailed procedure for chromatin immunoprecipitation (chip) to study the dna-protein interactions.