Super-enhancer mediated regulation of adult β-globin gene expression: the role of eRNA and Integrator

Super-enhancers (SEs) mediate high transcription levels of target genes. Previous studies have shown that SEs recruit transcription complexes and generate enhancer RNAs (eRNAs). We characterized transcription at the human and murine beta-globin locus control region (LCR) SE. We found that the human LCR is capable of recruiting transcription complexes independently from linked globin genes in transgenic mice. Furthermore, LCR hypersensitive site 2 (HS2) initiates the formation of bidirectional transcripts in transgenic mice and in the endogenous beta-globin gene locus in murine erythroleukemia (MEL) cells. HS2 3'eRNA is relatively unstable and remains in close proximity to the globin gene locus. Reducing the abundance of HS2 3'eRNA leads to a reduction in beta-globin gene transcription and compromises RNA polymerase II (Pol II) recruitment at the promoter. The Integrator complex has been shown to terminate eRNA transcription. We demonstrate that Integrator interacts downstream of LCR HS2. Inducible ablation of Integrator function in MEL or differentiating primary human CD34+ cells causes a decrease in expression of the adult beta-globin gene and accumulation of Pol II and eRNA at the LCR. The data suggest that transcription complexes are assembled at the LCR and transferred to the globin genes by mechanisms that involve Integrator mediated release of Pol II and eRNA from the LCR.

Automated summary

SEs mediate high transcription levels by recruiting transcription complexes and generating eRNAs. The LCR is able to recruit transcription complexes independently from linked genes, and HS2 initiates bidirectional transcription. Integrator complex plays a role in terminating eRNA transcription and interacts downstream of LCR HS2, affecting transcription of beta-globin genes.