Project description:Cytokines utilize the transcription factor STAT5 to control cell-specific and universal genes. In general, the magnitude of cell-restricted gene activation greatly exceeds that of universal genes, with a mechanistic explanation yet to be supplied. Genome-wide studies have identified putative STAT5-based mammary-specific enhancers and universal STAT5-controlled regulatory elements, an opportunity to investigate mechanisms underlying their differential response to cytokines. We have now interrogated the integrity and function of both categories of regulatory elements using biological and genetic approaches. During lactation, STAT5 occupies mammary-specific and universal cytokine-responsive elements. Following lactation, prolactin levels decline and STAT5-dependent enhancers at mammary-specific genes are decommissioned with 24 hours while universal regulatory complexes remain intact. These differential sensitivities are linked to STAT5 concentrations and the mammary-specific Stat5 autoregulatory enhancer. In its absence, mammary-specific enhancers, but not universal elements, fail to be fully established. Upon termination of lactation, STAT5 binding to a subset of mammary enhancers is substituted by STAT3. No STAT3 binding was observed at the most sensitive STAT5 enhancers, suggesting that upon hormone withdrawal their chromatin becomes inaccessible. This study, for the first time, provides molecular insight into the differential sensitivities of mammary-specific and universal cytokine-sensing enhancers.
Project description:STAT5, a member of the family of Signal Transducers and Activators of Transcription senses cytokines and controls the biology of cell lineages, including mammary, liver and T cells. Here we show that STAT5 activates lineage-specific and widely expressed genes through different mechanisms. STAT5 preferentially binds to promoter sequences of cytokine-responsive genes expressed across cell types and to putative enhancers of lineage-specific genes. While chromatin accessibility of STAT5-based enhancers was dependent on cytokine exposure, STAT5-responsive promoters of widely expressed target genes were generally constitutively accessible. While the contribution of STAT5 to enhancers is well established, its role on promoters is poorly understood. To address this we focused on Socs2, a widely expressed cytokine-sensing gene. Upon deletion of the STAT5 response elements from the Socs2 promoter, cytokine induction was abrogated, while basal activity remained intact. Our data suggest that promoter-bound STAT5 modulates cytokine responses and enhancer-bound STAT5 is mandatory for gene activation.
Project description:Signal Transducers and Activators of Transcription (STATs) are principal transcription factors downstream of cytokine receptors. Although STAT5A is expressed in most tissues it remains to be understood why its premier, non-redundant functions are restricted to prolactin-induced mammary gland development. We report that the ubiquitously expressed Stat5a/b locus is subject to lineage-specific transcriptional control in mammary epithelium. Genome-wide surveys of epigenetic status and transcription factor occupancy uncovered a putative mammary-specific enhancer within the intergenic sequences separating the two Stat5 genes. This region exhibited several hallmarks of genomic enhancers, including DNaseI hypersensitive sites, H3K27 acetylation and binding by GR and MED1. Mammary-specific STAT5 binding was obtained at two canonical STAT5 binding motifs. CRISPR/Cas9-mediated genome editing was used to delete these STAT5 binding sites in mice and determine their biological function. Mutant animals exhibited an 80% reduction of Stat5 levels in mammary epithelium and a concomitant reduction of STAT5-dependent gene expression. Transcriptome analysis identified a class of mammary-restricted genes that was particularly dependent on high STAT5 levels as a result of the intergenic enhancer. Taken together, the mammary-specific enhancer enables a positive feedback circuit that underlies the remarkable abundance of STAT5 and, in turn, controls the efficacy of STAT5-dependent mammary physiology. ChIP-seq for H3K27ac, RNA Pol II, and MED1 in mammary tissues at L1, and ChIP-seq for H3K27ac and GR in mammary tissues at p13. mRNA-seq in WT at L1, line B (GAS2 mutation only) and line C (both GAS1 and GAS2 mutations) at L1 in mammary tissues, and DNase-seq in WT mammary tissues at L1.
Project description:Signal Transducers and Activators of Transcription (STATs) are principal transcription factors downstream of cytokine receptors. Although STAT5A is expressed in most tissues it remains to be understood why its premier, non-redundant functions are restricted to prolactin-induced mammary gland development. We report that the ubiquitously expressed Stat5a/b locus is subject to lineage-specific transcriptional control in mammary epithelium. Genome-wide surveys of epigenetic status and transcription factor occupancy uncovered a putative mammary-specific enhancer within the intergenic sequences separating the two Stat5 genes. This region exhibited several hallmarks of genomic enhancers, including DNaseI hypersensitive sites, H3K27 acetylation and binding by GR and MED1. Mammary-specific STAT5 binding was obtained at two canonical STAT5 binding motifs. CRISPR/Cas9-mediated genome editing was used to delete these STAT5 binding sites in mice and determine their biological function. Mutant animals exhibited an 80% reduction of Stat5 levels in mammary epithelium and a concomitant reduction of STAT5-dependent gene expression. Transcriptome analysis identified a class of mammary-restricted genes that was particularly dependent on high STAT5 levels as a result of the intergenic enhancer. Taken together, the mammary-specific enhancer enables a positive feedback circuit that underlies the remarkable abundance of STAT5 and, in turn, controls the efficacy of STAT5-dependent mammary physiology.
Project description:The mammary luminal lineage relies on the common cytokine-sensing transcription factor STAT5 to establish super-enhancers during pregnancy and activate mammary genes required for the nutrition of the offspring. Exploiting progressive differentiation during lactation, we investigated how hormonal cues shape an evolving enhancer landscape and impact the biology of mammary cells. Employing ChIP-seq, we uncover a changing transcription factor occupancy at mammary enhancers. Using mouse genetics, we demonstrate changing biological properties of enhancers as lactation progresses, with individual enhancers gaining strength and an abolished need for the Wap seed enhancer. We further investigated whether permissive chromatin facilitates cell-specific transcription factor binding. Wap enhancers translocated into the widely expressed neighboring Ramp3 gene retained their mammary-specificity and failed to activate the receptive Ramp3 gene in non-mammary tissues. Our studies unveil a previously unrecognized progressive enhancer landscape, in which structurally equivalent components serve unique and differentiation-specific functions. While enhancer redundancy has been suggested and demonstrated for many genes, components of the cytokine-responsive mammary tripartite Wap super-enhancer display a remarkable specificity.
Project description:The mammary luminal lineage relies on the common cytokine-sensing transcription factor STAT5 to establish super-enhancers during pregnancy and activate mammary genes required for the nutrition of the offspring. Exploiting progressive differentiation during lactation, we investigated how hormonal cues shape an evolving enhancer landscape and impact the biology of mammary cells. Employing ChIP-seq, we uncover a changing transcription factor occupancy at mammary enhancers. Using mouse genetics, we demonstrate changing biological properties of enhancers as lactation progresses, with individual enhancers gaining strength and an abolished need for the Wap seed enhancer. We further investigated whether permissive chromatin facilitates cell-specific transcription factor binding. Wap enhancers translocated into the widely expressed neighboring Ramp3 gene retained their mammary-specificity and failed to activate the receptive Ramp3 gene in non-mammary tissues. Our studies unveil a previously unrecognized progressive enhancer landscape, in which structurally equivalent components serve unique and differentiation-specific functions. While enhancer redundancy has been suggested and demonstrated for many genes, components of the cytokine-responsive mammary tripartite Wap super-enhancer display a remarkable specificity.
Project description:Super-enhancers comprise of dense transcription factor platforms highly enriched for active chromatin marks. A paucity of functional data led us to investigate their role in the mammary gland, an organ characterized by exceptional gene regulatory dynamics during pregnancy. ChIP-Seq for the master regulator STAT5, the glucocorticoid receptor, H3K27ac and MED1, identified 440 mammary-specific super-enhancers, half of which were associated with genes activated during pregnancy. We interrogated the Wap super-enhancer, generating mice carrying mutations in STAT5 binding sites within its three constituent enhancers. Individually, only the most distal site displayed significant enhancer activity. However, combinatorial mutations showed that the 1,000-fold gene induction relied on all enhancers. Disabling the binding sites of STAT5, NFIB and ELF5 in the proximal enhancer incapacitated the entire super-enhancer, suggesting an enhancer hierarchy. The identification of mammary-specific super-enhancers and the mechanistic exploration of the Wap locus provide insight into the complexity of cell-specific and hormone-regulated genes. ChIP-Seq for STAT5A, GR, H3K27ac, MED1, NFIB, ELF5, RNA Pol II, and H3K4me3 in wild type (WT) mammary tissues at day one of lactation (L1), and ChIP-Seq for STAT5A, GR, H3K27ac, MED1, NFIB, ELF5, and H3K4me3 in WT mammary tissues at day 13 of pregnancy (p13). ChIP-Seq for STAT5A, GR, H3K27a in Wap-delE1a, -delE1b, -delE1c, -delE2 and -delE3 mutant mammary tissues at L1, and ChIP-Seq for NFIB and ELF5 in Wap-delE1b and -delE1c mutant mammary tissues at L1. ChIP-Seq for H3K4me3 in mammary-epthelial cells at p13 and L1. DNase-seq in WT mammary tissues at L1 and DNase-seq in Wap-delE1a, -delE1c, and -delE3 mutant mammary tissues at L1.
Project description:Super-enhancers comprise of dense transcription factor platforms highly enriched for active chromatin marks. A paucity of functional data led us to investigate their role in the mammary gland, an organ characterized by exceptional gene regulatory dynamics during pregnancy. ChIP-Seq for the master regulator STAT5, the glucocorticoid receptor, H3K27ac and MED1, identified 440 mammary-specific super-enhancers, half of which were associated with genes activated during pregnancy. We interrogated the Wap super-enhancer, generating mice carrying mutations in STAT5 binding sites within its three constituent enhancers. Individually, only the most distal site displayed significant enhancer activity. However, combinatorial mutations showed that the 1,000-fold gene induction relied on all enhancers. Disabling the binding sites of STAT5, NFIB and ELF5 in the proximal enhancer incapacitated the entire super-enhancer, suggesting an enhancer hierarchy. The identification of mammary-specific super-enhancers and the mechanistic exploration of the Wap locus provide insight into the complexity of cell-specific and hormone-regulated genes.
Project description:Cytokines control the expression of common and cell-specific genes through the transcription factor STAT5. In mammary tissue specifically, expression of approximately 570 genes is induced during pregnancy by prolactin through STAT5, which binds to putative regulatory sequences. We have now asked whether mammary-specific induction of these genes can be linked to the presence of additional transcription factors, which would act in concert with STAT5. RNA-seq analysis at parturition identified 370 genes that were under NFIB control. Notably, 75% of these genes, encoding proteins linked to the differentiation of mammary epithelium, were also regulated by STAT5. This study demonstrates that the STAT5-NFIB module is an essential part of genes that define differentiation and function of the mammary gland. Expression profiling by high throughput sequencing in wild-type (WT) and Nfib-null (KO) mammary gland tissues
Project description:Establishment and differentiation of mammary alveoli during pregnancy are controlled by prolactin through the transcription factor STAT5. As pregnancy progresses mammary signature genes are activated in a defined temporal order, which coincides with the recruitment of STAT5 to respective regulatory sequences. This study addressed the question whether the methyltransferase and transcriptional co-activator EZH2 controls the differentiation clock of mammary epithelium. Ablation of Ezh2 from mammary stem cells resulted in precocious differentiation of alveolar epithelium during pregnancy and the activation of mammary-specific STAT5 target genes. This coincided with enhanced occupancy by STAT5, EZH1 and Pol II to these loci. Limited activation of differentiation-specific genes was also observed in mammary epithelium lacking both EZH2 and STAT5, suggesting a modulating but not mandatory role for STAT5. Notably, loss of EZH2 did not result in overt changes in genome-wide and gene-specific H3K27me3 patterns, suggesting that enhanced EZH1 recruitment can compensate for the loss of EZH2. Differentiated mammary epithelia failed to form in the combined absence of EZH1 and EZH2. Transplantation experiments failed to demonstrate a role for EZH2 in the biology of mammary stem and progenitor cells. In summary, while EZH1 and EZH2 serve redundant functions in the establishment of H3K27me3 and formation of mammary alveoli, the presence of EZH2 is required to obtain controlled temporal differentiation of mammary epithelium. mRNA-seq in WT;MMTV-Cre (Control) at p13 and p18, E1-/- (E1KO), Ezh2f/f;MMTV-Cre(E2KO), Stat5f/f;MMTV-Cre(S5KO), and Ezh2f/f;Stat5f/f;MMTV-Cre (E2S5DKO) at p13 mammary tissues. ChIP-seq for H3K27me3, STAT5, EZH1, EZH2 and PolII in mammary tissues at p13