Nuclear receptors are a class of proteins found within cells that play a crucial role in regulating gene expression. They act as sensors for various hormones and other signaling molecules, such as steroids, thyroid hormones, and retinoids. When these molecules bind to nuclear receptors, the receptors undergo a change in shape, allowing them to interact with specific regions of DNA and influence the transcription of target genes. These receptors are essential for many physiological processes, including metabolism, development, and immune response. By modulating gene activity, nuclear receptors help maintain homeostasis and respond to environmental changes. Their dysfunction can lead to various diseases, including cancer and metabolic disorders.