Transcription factor recruitment to genomic sites of action is primarily due to direct protein:DNA interactions. The subsequent recruitment of coregulatory complexes leads to either transcriptional ...activation or repression. In contrast to this canonical scheme, some transcription factors, such as the glucocorticoid receptor (GR), behave as transcriptional repressors when recruited to target genes through protein tethering. We have investigated the genome-wide prevalence of tethering between GR and Stat3 and found nonreciprocal interactions, namely that GR tethering to DNA-bound Stat3 results in transcriptional repression, whereas Stat3 tethering to GR results in synergism. Further, other schemes of GR and Stat3 corecruitment to regulatory modules result in transcriptional synergism, including neighboring and composite binding sites. The results indicate extensive transcriptional interactions between Stat3 and GR; further, they provide a genome-wide assessment of transcriptional regulation by tethering and a molecular basis for integration of signals mediated by GR and Stats in health and disease.
► Extensive cooperative genomic recruitment of GR and Stat3 ► Binding of GR and Stat3 to neighboring DNA sites results in transcriptional synergism ► Stat3 tethering to GR is associated with transcriptional synergism ► GR tethering to Stat3 is linked to trans-repression by GR
Translation is a basic cellular process and its capacity is adapted to cell function. In particular, secretory cells achieve high protein synthesis levels without triggering the protein stress ...response. It is unknown how and when translation capacity is increased during differentiation. Here, we show that the transcription factor Creb3l2 is a scaling factor for translation capacity in pituitary secretory cells and that it directly binds ~75% of regulatory and effector genes for translation. In parallel with this cell-autonomous mechanism, implementation of the physiological UPR pathway prevents triggering the protein stress response. Knockout mice for Tpit, a pituitary differentiation factor, show that Creb3l2 expression and its downstream regulatory network are dependent on Tpit. Further, Creb3l2 acts by direct targeting of translation effector genes in parallel with signaling pathways that otherwise regulate protein synthesis. Expression of Creb3l2 may be a useful means to enhance production of therapeutic proteins.
In mammals, circadian oscillators reside not only in the suprachiasmatic nucleus of the brain, which harbors the central pacemaker, but also in most peripheral tissues. Here, we show that the ...glucocorticoid hormone analog dexamethasone induces circadian gene expression in cultured rat-1 fibroblasts and transiently changes the phase of circadian gene expression in liver, kidney, and heart. However, dexamethasone does not affect cyclic gene expression in neurons of the suprachiasmatic nucleus. This enabled us to establish an apparent phase-shift response curve specifically for peripheral clocks in intact animals. In contrast to the central clock, circadian oscillators in peripheral tissues appear to remain responsive to phase resetting throughout the day.
The anterior and intermediate lobes of the pituitary gland derive from the surface ectoderm. They provide a simple system to assess mechanisms of developmental identity established by tissue ...determinants. Each lobe contains a lineage expressing the hormone precursor pro-opiomelanocortin (POMC): the corticotropes and melanotropes. The T-box transcription factor Tpit controls terminal differentiation of both lineages. We now report on the unique role of Pax7 as a selector of intermediate lobe and melanotrope identity. Inactivation of the Pax7 gene results in loss of melanotrope gene expression and derepression of corticotrope genes. Pax7 acts by remodeling chromatin and allowing Tpit binding to a new subset of enhancers for activation of melanotrope-specific genes. Thus, the selector function of Pax7 is exerted through pioneer transcription factor activity. Genome-wide, the Pax7 pioneer activity is preferentially associated with composite binding sites that include paired and homeodomain motifs. Pax7 expression is conserved in human and dog melanotropes and defines two subtypes of pituitary adenomas causing Cushing's disease. In summary, expression of Pax7 provides a unique tissue identity to the pituitary intermediate lobe that alters Tpit-driven differentiation through pioneer and classical transcription factor activities.
The treatment of cultured rat-1 fibroblasts or H35 hepatoma cells with high concentrations of serum induces the circadian expression of various genes whose transcription also oscillates in living ...animals. Oscillating genes include
rper1 and
rper2(rat homologs of the
Drosophila clock gene
period), and the genes encoding the transcription factors Rev-Erbα, DBP, and TEF. In rat-1 fibroblasts, up to three consecutive daily oscillations with an average period length of 22.5 hr could be recorded. The temporal sequence of the various mRNA accumulation cycles is the same in cultured cells and in vivo. The serum shock of rat-1 fibroblasts also results in a transient stimulation of c-
fos and
rper expression and thus mimics light-induced immediate-early gene expression in the suprachiasmatic nucleus.
In mammals, all overt circadian rhythms are thought to be coordinated by a central pacemaker residing in the hypothalamic suprachiasmatic nucleus (SCN) 1. The phase of this pacemaker is entrained by ...photic cues via the retino-hypothalamic tract. Circadian clocks probably rely on a feedback loop in the expression of certain clock genes (reviewed in 2,3). Surprisingly, however, such molecular oscillators are not only operative in pacemaker cells, such as SCN neurons, but also in many peripheral tissues and even in cell lines kept in vitro4–7. For example, a serum shock can induce circadian gene expression in cultured Rat-1 fibroblasts 5. This treatment also results in a rapid surge of expression of the clock genes Per1 and Per2, similar to that observed in the SCNs of animals receiving a light pulse 8–10. Serum induction of Per1 and Per2 transcription does not require ongoing protein synthesis 5 and must therefore be accomplished by direct signaling pathways. Here, we show that cAMP, protein kinase C, glucocorticoid hormones and Ca2+ can all trigger a transient surge of Per1 transcription and elicit rhythmic gene expression in Rat-1 cells. We thus suspect that the SCN pacemaker may exploit multiple chemical cues to synchronize peripheral oscillators in vivo.
Cell-specific expression of the pituitary proopiomelanocortin (POMC) gene depends on the combinatorial action of a large number of DNA-binding transcription factors (TFs). These include general and ...cell-restricted factors, as well as factors that act as effectors of signaling pathways. We have previously defined in the distal POMC promoter a composite regulatory element that contains targets for basic helix-loop-helix TFs conferring cell specificity and for NGFI-B orphan nuclear receptors that are responsive to CRH signaling and to glucocorticoid negative feedback. These factors act on neighboring regulatory elements, the Ebox(Neuro) and NurRE, respectively. Currently, the Ebox(Neuro) is thought to be the target of NeuroD1 during fetal development, but this factor may not account for activity in the adult pituitary; it is also unknown whether the NurRE and NGFI-B-related factors are active before establishment of the hypothalamic-pituitary portal system. In order to assess the importance of these regulatory elements and their cognate TFs throughout pituitary organogenesis and in the adult, we have assessed the activity of mutant POMC promoters in transgenic mice throughout development. These experiments indicate that the Ebox(Neuro) and cognate basic helix-loop-helix factors are required throughout development and in the adult gland, beyond expression of NeuroD1. Similarly, the data reveal sustained importance of the NurRE and its cognate factors throughout pituitary development. These data contrast the sustained dependence throughout development on the same regulatory elements with the highly dynamic patterns of TF expression and the modulation of their activity in response to signaling pathways.
Meis1 and Meis2 are homeodomain transcription factors that regulate organogenesis through cooperation with Hox proteins. Elimination of Meis genes after limb induction has shown their role in limb ...proximo-distal patterning; however, limb development in the complete absence of Meis function has not been studied. Here, we report that Meis1/2 inactivation in the lateral plate mesoderm of mouse embryos leads to limb agenesis. Meis and Tbx factors converge in this function, extensively co-binding with Tbx to genomic sites and co-regulating enhancers of Fgf10, a critical factor in limb initiation. Limbs with three deleted Meis alleles show proximal-specific skeletal hypoplasia and agenesis of posterior skeletal elements. This failure in posterior specification results from an early role of Meis factors in establishing the limb antero-posterior prepattern required for Shh activation. Our results demonstrate roles for Meis transcription factors in early limb development and identify their involvement in previously undescribed interaction networks that regulate organogenesis.
Pioneer transcription factors are characterized by having the unique property of enabling the opening of closed chromatin sites, for implementation of cell fates. We previously found that the pioneer ...Pax7 specifies melanotrope cells through deployment of an enhancer repertoire, which allows binding of Tpit, a nonpioneer factor that determines the related lineages of melanotropes and corticotropes. Here, we investigate the relation between these two factors in the pioneer mechanism. Cell-specific gene expression and chromatin landscapes are defined by scRNAseq and chromatin accessibility profiling. We find that in vivo deployment of the melanotrope enhancer repertoire and chromatin opening requires both Pax7 and Tpit. In cells, binding of heterochromatin targets by Pax7 is independent of Tpit but Pax7-dependent chromatin opening requires Tpit. The present work shows that pioneer core properties are limited to the ability to recognize heterochromatin targets and facilitate nonpioneer binding. Chromatin opening per se may be provided through cooperation with nonpioneer factors.
For many years, neurons of the suprachiasmatic nucleus (SCN) in the hypothalamus were thought to contain the unique mammalian clock controlling circadian rhythmicity of peripheral tissues via neural ...and humoral signals. Surprisingly, the cloning and characterisation of mammalian clock genes have revealed that they are expressed in a circadian manner throughout the body. It is generally accepted now that peripheral cells contain a circadian clock which is similar to the one present in SCN neurons, although only the latter seems to be self-sustained. It is still unclear how these peripheral clocks are synchronised by the central SCN clock, albeit humoral signals appear to be crucial. Interestingly, peripheral clocks can be uncoupled from the central clock in particular conditions such as restricted-feeding, allowing peripheral tissues to adapt themselves to cues incompatible to other cues perceived by the SCN (mainly the photoperiod). Whereas circadian clocks have been intensively dissected, little is known about the mechanisms by which these clocks regulate the expression of clock-controlled genes. Direct regulation for some of them by the products of clock genes was recently documented, but this probably represents the exception rather than the rule. We should soon be able to describe complete circadian transcriptional cascades from clock genes to enzymes and structural proteins. In addition to circadian humoral and neural signals, these cascades should help us to understand how gene expression, physiology and behaviour are influenced by the rotation of the Earth around its axis.
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