Emergence of a New Gene from an Intergenic Region

It is generally assumed that new genes would arise by gene duplication mechanisms, because the signals for regulation and transcript processing would be unlikely to evolve in parallel with a new gene function [1, 2]. We have identified here a transcript in the house mouse ( Mus musculus) that has arisen within the past 2.5–3.5 million years in a large intergenic region. The region is present in many mammals, including humans, allowing us to exclude the involvement of gene duplication, transposable elements, or other genome rearrangements, which are typically found for other cases of newly evolved genes [3–8]. The gene has three exons, shows alternative splicing, and is specifically expressed in postmeiotic cells of the testis. The transcript is restricted to species within the genus Mus and its emergence correlates with indel mutations in the 5′ regulatory region of the transcript. A recent selective sweep is associated with the transcript region in M. m. musculus populations. A knockout in the laboratory strain BL6 results in reduced sperm motility and reduced testis weight. Our results show that cryptic signals for transcript regulation and processing exist in intergenic regions and can become the basis for the evolution of a new functional gene.