Specialized proteins in the nucleus that are involved in the regulation of gene activity in response to hormones and other signals. It has been estimated that approximately 30,000 genes are expressed in the human genome. The transcription of these genes into messenger ribonucleic acid (mRNA) and their subsequent translation into protein determines the identity and function of each cell in the human body. The balance between sickness and health requires that transcription of these genes be precisely regulated in response to both physiological and environmental changes. A variety of signaling strategies have evolved to coordinate the body's transcriptional response to such events. The nuclear hormone receptors represent one of the largest family of proteins that directly regulate transcription in response to hormones and other ligands (chemical entities that bind to and activate the receptor).