Nuclear receptors (NRs) are transcription factors with deoxyribonucleic acid (DNA)-binding and ligand-receptor domains. When activated by ligands, they bind to the regulatory regions of target genes to regulate transcription. NR genes comprise relatively large gene families derived from a single metazoan parent gene through evolutionary duplication and divergence, which often produces duplication (unprocessed) pseudogenes. However, no NR duplication pseudogenes have been found in genomes examined to date. A small number of NR retropseudogenes (processed pseudogenes), and a single unitary pseudogene have been identified in the annotated human, chimpanzee, mouse and rat genomes. The unitary pseudogene (FXR) is exclusive to catarrhines and arose via mutational inactivation of the FXR gene, which is an active gene in murids. The human-specific ERR+ pseudogene arose through duplication of a DNA segment containing the ERR–retropseudogene and is an example of a duplication retropseudogene. The murid Rev-erb and LRH1 pseudogenes are examples semiprocessed retropseudogenes.

Key concepts

• There are relatively few nuclear receptor pseudogenes in vertebrate genomes.
  
• Identified nuclear receptor genes consist of retropseudogenes and a single unitary pseudogene.