Genome binding/occupancy profiling by high throughput sequencing
Summary
Enhancers are transcription factor platforms that synergize with promoters to activate gene expression. While genome-wide chromatin studies can predict enhancers, only experimental genetics can reveal their in vivo significance and the respective contribution of individual transcription factors. Here we investigate the regulation of the Csn1s2b gene whose expression in the mouse mammary gland is induced several thousand-fold during pregnancy and lactation. Using ChIP-seq for activating histone marks and transcription factors, we identified candidate enhancers distal to the promoter and within an intron and one super-enhancer separated from the Csn1s2b gene by the Prr27 gene. Using experimental mouse genetics, we dissected the complex lactation-specific distal enhancer bound by the prolactin-activated transcription factor STAT5 and the mammary-enriched NFIB and the glucocorticoid receptor. Deletion of the canonical binding motifs for NFIB and STAT5, individually and combined, had a limited biological impact. Additional deletions revealed the importance of a non-canonical STAT5 binding site for enhancer activity throughout lactation. In contrast, the intronic enhancer activated gene expression only in late pregnancy and early lactation, likely by interacting with the distal enhancer. A downstream super-enhancer, which physically interacts with the distal enhancer, was required for the functional establishment of the Csn1s2b promoter and gene activation. Lastly, NFIB binding in the promoter region fine-tuned Csn1s2b expression. Our study provides comprehensive insight into the anatomy and biology of regulatory elements spanning 70 bp that employ the JAK/STAT signaling pathway and activate gene expression several hundred-fold during lactation.
Overall design
ChIP-seq for TFs and histone markers in the mammary tissues of wild type and mutant mice for Csn1s2b regulatory elements at day one and ten of lactation.
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