Reactivation of developmentally silenced globin genes through genomic deletions reveals that enhancer distance matters
The human genome contains regulatory DNA elements, enhancers, that can activate gene transcription over long chromosomal distances. Here, we show that enhancer distance can be critical for gene silencing. We demonstrate that linear recruitment of the normally distal HBB super-enhancer to developmentally silenced HBG promoters, through deletion or inversion of intervening DNA sequences, results in strongly reactivated HBG expression in adult erythroid cells and ex vivo differentiated hematopoietic stem and progenitor cells. A similar observation is made in the HBA locus, where deletion-to-recruit of the distal enhancer strongly reactivates embryonic HBZ expression. Overall, our work assigns function to seemingly non-regulatory genomic segments: by providing linear separation they may support genes to autonomously control their transcriptional response to distal enhancers.