Gene regulation by steroid hormones

The ability of cells to specify the fraction of their genetic information that they express in a particular spatiotemporal context is essential for adaptation to the changing conditions of their surroundings. In higher organisms, cells must respond to stimuli from the outer world and to signals from other cells directed to coordinate their state of activity for the proper development and functioning of the whole animal. Many of these signals impinge on receptors located at the cell membrane, where they elicit changes in the intracellular concentration of key molecules, second messengers, that ultimately modulate the expression of genetic programs. The signal transduction mechanism is simpler in the case of molecules acting through nuclear receptors able to recognize the signal and to interact directly with the nuclear genome. To this class belong the steroid hormones that influence the expression of a great variety of genes in many different cells.