Overcoming challenges and dogmas to understand the functions of pseudogenes

Pseudogenes are defined as regions of the genome that contain defective copies of genes. They exist across almost all forms of life, and in mammalian genomes are annotated in similar numbers to recognized protein-coding genes. Although often presumed to lack function, growing numbers of pseudogenes are being found to play important biological roles. In consideration of their evolutionary origins and inherent limitations in genome annotation practices, we posit that pseudogenes have been classified on a scientifically unsubstantiated basis. We reflect that a broad misunderstanding of pseudogenes, perpetuated in part by the pejorative inference of the 'pseudogene' label, has led to their frequent dismissal from functional assessment and exclusion from genomic analyses. With the advent of technologies that simplify the study of pseudogenes, we propose that an objective reassessment of these genomic elements will reveal valuable insights into genome function and evolution. In this Perspective article, Cheetham, Faulkner and Dinger describe our latest understanding of pseudogenes, which are typically defined as defective copies of regular genes. They argue that being open minded about potential functionality, as well as carefully designing functional studies, will lead to a growing appreciation of emerging functional roles of these understudied elements.