Nuclear receptors are a type of protein found inside cells that play a crucial role in regulating gene expression. They act like switches, turning genes on or off in response to specific signals, such as hormones or other molecules. This process helps control various bodily functions, including metabolism, development, and immune responses. These receptors can bind to steroid hormones, like estrogen and testosterone, as well as thyroid hormones and retinoic acid. Once activated, they move to the cell nucleus, where they interact with DNA to influence how genes are expressed, ultimately affecting how cells behave and function in the body.