Towards a comprehensive catalogue of validated and target-linked human enhancers

The human gene catalogue is essentially complete, but we lack an equivalently vetted inventory of bona fide human enhancers. Hundreds of thousands of candidate enhancers have been nominated via biochemical annotations; however, only a handful of these have been validated and confidently linked to their target genes. Here we review emerging technologies for discovering, characterizing and validating human enhancers at scale. We furthermore propose a new framework for operationally defining enhancers that accommodates the heterogeneous and complementary results that are emerging from reporter assays, biochemical measurements and CRISPR screens. In this Review, Gasperini, Tome and Shendure discuss the evolving definitions of transcriptional enhancers, as well as diverse modern experimental tools to identify them. The authors describe how these diverse mindsets and methods provide differing but complementary insights into enhancers, each with notable strengths and caveats. They discuss how such views and approaches might be combined in a comprehensive catalogue of functional enhancers.