Caenorhabditis elegans mediator complexes are required for developmental-specific transcriptional activation

BmMed6 modulates mating behavior by ORs and antennae structural genes in the silkworm

Gene expression is under strict and precise control to regulate organism development and maintain various physiological functions. The Mediator complex is a regulator of gene transcription. Our study focused on BmMed6, a component of the Mediator complex in the Bombyx mori. We construct BmMed6 mutants using the CRISPR-Cas9 system. The mutants exhibited abnormal growth patterns in their antennae, which limited their mating behavior. RNA-seq and gene expression analysis have revealed that the expression of genes associated with structural constituents of the cuticle in the antennae of the mutant was aberrant. Moreover, the deficiency of BmMed6 also caused the downregulation of olfactory receptor genes. Our findings offer novel insights into the biological role of BmMed6 in antenna growth, revealing its crucial role in regulating antenna structure and olfactory gene expression to influence mating behaviors. This discovery identifies BmMed6 as a viable new target gene for pest control.

Upregulation of MED7 was associated with progression in hepatocellular carcinoma

OBJECTIVE

MED subunits have been reported to be associated with various types of tumors, however, the potential role of MED7 in hepatocellular carcinoma (HCC) was still unclear. The aim of the study was to explore the role of MED7 in HCC.

METHODS

In this study, MED7 mRNA expression levels between HCC and adjacent normal tissues were first analyzed by several public datasets. Then we utilized a tissue microarray (TMA) to investigate the clinical role of MED7 in HCC by immunohistochemistry (IHC). Meanwhile, the potential mechanisms of MED7 based on gene-gene correlation analyses were also explored.

RESULTS

High mRNA level of MED7 correlated with advanced stage and worse grade of differentiation. IHC results showed that MED7 protein level was upregulated in HCC and associated with Edmondson grade and Microvascular invasion in 330 cases of HCC. GO (Gene Ontology) and KEGG (Kyoto Encyclopedia of Genes and Genomes) analysis revealed that MED7 co-expressed genes participate primarily in ribonucleoprotein complex biogenesis, protein targeting, mRNA processing and nucleoside triphosphate metabolic process et cetera. Further analysis also revealed that MED7 mRNA level has significant correlation with immune cells infiltration levels.

CONCLUSION

MED7 was upregulated in HCC and correlated with progression of HCC. Meanwhile, MED7 may promote HCC through participating in multiple gene networks to influence tumorigenesis as well as immune response in HCC microenvironment.

Role of the Mediator Complex and MicroRNAs in Breast Cancer Etiology

Transcriptional coactivators play a key role in RNA polymerase II transcription and gene regulation. One of the most important transcriptional coactivators is the Mediator (MED) complex, which is an evolutionary conserved large multiprotein complex. MED transduces the signal between DNA-bound transcriptional activators (gene-specific transcription factors) to the RNA polymerase II transcription machinery to activate transcription. It is known that MED plays an essential role in ER-mediated gene expression mainly through the MED1 subunit, since estrogen receptor (ER) can interact with MED1 by specific protein–protein interactions; therefore, MED1 plays a fundamental role in ER-positive breast cancer (BC) etiology. Additionally, other MED subunits also play a role in BC etiology. On the other hand, microRNAs (miRNAs) are a family of small non-coding RNAs, which can regulate gene expression at the post-transcriptional level by binding in a sequence-specific fashion at the 3′ UTR of the messenger RNA. The miRNAs are also important factors that influence oncogenic signaling in BC by acting as both tumor suppressors and oncogenes. Moreover, miRNAs are involved in endocrine therapy resistance of BC, specifically to tamoxifen, a drug that is used to target ER signaling. In metazoans, very little is known about the transcriptional regulation of miRNA by the MED complex and less about the transcriptional regulation of miRNAs involved in BC initiation and progression. Recently, it has been shown that MED1 is able to regulate the transcription of the ER-dependent miR-191/425 cluster promoting BC cell proliferation and migration. In this review, we will discuss the role of MED1 transcriptional coactivator in the etiology of BC and in endocrine therapy-resistance of BC and also the contribution of other MED subunits to BC development, progression and metastasis. Lastly, we identified miRNAs that potentially can regulate the expression of MED subunits.

Overexpression of OsMed16 Inhibits the Growth of Rice and Causes Spontaneous Cell Death

The Mediator complex transduces information from the DNA-bound transcription factors to the RNA polymerase II transcriptional machinery. Research on plant Mediator subunits has primarily been performed in Arabidopsis, while very few of them have been functionally characterized in rice. In this study, the rice Mediator subunit 16, OsMed16, was examined. OsMed16 encodes a putative protein of 1301 amino acids, which is longer than the version previously reported. It was expressed in various rice organs and localized to the nucleus. The knockout of OsMed16 resulted in rice seedling lethality. Its overexpression led to the retardation of rice growth, low yield, and spontaneous cell death in the leaf blade and sheath. RNA sequencing suggested that the overexpression of OsMed16 altered the expression of a large number of genes. Among them, the upregulation of some defense-related genes was verified. OsMed16 can regulate the expression of a wealth of genes, and alterations in its expression have a profound impact on plant growth, development, and defense responses in rice.

Integrated analysis of the critical region 5p15.3-p15.2 associated with cri-du-chat syndrome

Cri-du-chat syndrome (CdCs) is one of the most common contiguous gene syndromes, with an incidence of 1:15,000 to 1:50,000 live births. To better understand the etiology of CdCs at the molecular level, we investigated theprotein-protein interaction (PPI) network within the critical chromosomal region 5p15.3-p15.2 associated with CdCs using systemsbiology. Data were extracted from cytogenomic findings from patients with CdCs. Based on clinical findings, molecular characterization of chromosomal rearrangements, and systems biology data, we explored possible genotype-phenotype correlations involving biological processes connected with CdCs candidate genes. We identified biological processes involving genes previously found to be associated with CdCs, such as TERT, SLC6A3, and CTDNND2, as well as novel candidate proteins with potential contributions to CdCs phenotypes, including CCT5, TPPP, MED10, ADCY2, MTRR, CEP72, NDUFS6, and MRPL36. Although further functional analyses of these proteins are required, we identified candidate proteins for the development of new multi-target genetic editing tools to study CdCs. Further research may confirm those that are directly involved in the development of CdCs phenotypes and improve our understanding of CdCs-associated molecular mechanisms.

The MED7 subunit paralogs of Mediator function redundantly in development of etiolated seedlings in Arabidopsis

MED7 is a subunit of the Mediator middle module and is encoded by two paralogs in Arabidopsis. We generated MED7 silenced lines using RNAi to study its impact on Arabidopsis growth and development. Compared with wild type, etiolated seedlings of the MED7 silenced lines exhibited reduced hypocotyl length caused by reduced cell elongation when grown in the dark. The hypocotyl length phenotype was rescued by exogenously supplied brassinosteroid. In addition, MED7 silenced seedlings exhibited defective hook opening in the dark as well as defective cotyledon expansion in the presence of the brassinosteroid inhibitor brassinazole. Whole transcriptome analysis on etiolated seedlings using RNA sequencing revealed several genes known to be regulated by auxin and brassinosteroids, and a broad range of cell wall-related genes that were differentially expressed in the MED7 silenced lines. This was especially evident for genes involved in cell wall extension and remodeling, such as EXPANSINs and XTHs. Conditional complementation with each MED7 paralog individually restored the hypocotyl phenotype as well as the gene expression defects. Additionally, conditional expression of MED7 had no effects that were independent of the Mediator complex on the observed phenotypes. We concluded that the MED7 paralogs function redundantly in regulating genes required for the normal development of etiolated Arabidopsis seedlings.

Mediator complex (MED) 7: a biomarker associated with good prognosis in invasive breast cancer, especially ER+ luminal subtypes

Background

Mediator complex (MED) proteins have a key role in transcriptional regulation, some interacting with the oestrogen receptor (ER). Interrogation of the METABRIC cohort suggested that MED7 may regulate lymphovascular invasion (LVI). Thus MED7 expression was assessed in large breast cancer (BC) cohorts to determine clinicopathological significance.

Methods

MED7 gene expression was investigated in the METABRIC cohort (n = 1980) and externally validated using bc-GenExMiner v4.0. Immunohistochemical expression was assessed in the Nottingham primary BC series (n = 1280). Associations with clinicopathological variables and patient outcome were evaluated.

Results

High MED7 mRNA and protein expression was associated with good prognostic factors: low grade, smaller tumour size, good NPI, positive hormone receptor status (p < 0.001), and negative LVI (p = 0.04) status. Higher MED7 protein expression was associated with improved BC-specific survival within the whole cohort and ER+/luminal subgroup. Pooled MED7 gene expression data in the external validation cohort confirmed association with better survival, corroborating with the protein expression. On multivariate analysis, MED7 protein was independently predictive of longer BC-specific survival in the whole cohort and Luminal A subtype (p < 0.001).

Conclusions

MED7 is an important prognostic marker in BC, particularly in ER+luminal subtypes, associated with improved survival and warrants future functional analysis.

Plant Mediator complex and its critical functions in transcription regulation

The Mediator complex is an important component of the eukaryotic transcriptional machinery. As an essential link between transcription factors and RNA polymerase II, the Mediator complex transduces diverse signals to genes involved in different pathways. The plant Mediator complex was recently purified and comprises conserved and specific subunits. It functions in concert with transcription factors to modulate various responses. In this review, we summarize the recent advances in understanding the plant Mediator complex and its diverse roles in plant growth, development, defense, non-coding RNA production, response to abiotic stresses, flowering, genomic stability and metabolic homeostasis. In addition, the transcription factors interacting with the Mediator complex are also highlighted.

Development and validation of a mixed-tissue oligonucleotide DNA microarray for Atlantic bluefin tuna, Thunnus thynnus (Linnaeus, 1758)

BACKGROUND

The largest of the tuna species, Atlantic bluefin tuna (Thunnus thynnus), inhabits the North Atlantic Ocean and the Mediterranean Sea and is considered to be an endangered species, largely a consequence of overfishing. T. thynnus aquaculture, referred to as fattening or farming, is a capture based activity dependent on yearly renewal from the wild. Thus, the development of aquaculture practices independent of wild resources can provide an important contribution towards ensuring security and sustainability of this species in the longer-term. The development of such practices is today greatly assisted by large scale transcriptomic studies.

RESULTS

We have used pyrosequencing technology to sequence a mixed-tissue normalised cDNA library, derived from adult T. thynnus. A total of 976,904 raw sequence reads were assembled into 33,105 unique transcripts having a mean length of 893 bases and an N50 of 870. Of these, 33.4% showed similarity to known proteins or gene transcripts and 86.6% of them were matched to the congeneric Pacific bluefin tuna (Thunnus orientalis) genome, compared to 70.3% for the more distantly related Nile tilapia (Oreochromis niloticus) genome. Transcript sequences were used to develop a novel 15 K Agilent oligonucleotide DNA microarray for T. thynnus and comparative tissue gene expression profiles were inferred for gill, heart, liver, ovaries and testes. Functional contrasts were strongest between gills and ovaries. Gills were particularly associated with immune system, signal transduction and cell communication, while ovaries displayed signatures of glycan biosynthesis, nucleotide metabolism, transcription, translation, replication and repair.

CONCLUSIONS

Sequence data generated from a novel mixed-tissue T. thynnus cDNA library provide an important transcriptomic resource that can be further employed for study of various aspects of T. thynnus ecology and genomics, with strong applications in aquaculture. Tissue-specific gene expression profiles inferred through the use of novel oligo-microarray can serve in the design of new and more focused transcriptomic studies for future research of tuna physiology and assessment of the welfare in a production environment.

Evolution of disorder in Mediator complex and its functional relevance

Mediator, an important component of eukaryotic transcriptional machinery, is a huge multisubunit complex. Though the complex is known to be conserved across all the eukaryotic kingdoms, the evolutionary topology of its subunits has never been studied. In this study, we profiled disorder in the Mediator subunits of 146 eukaryotes belonging to three kingdoms viz., metazoans, plants and fungi, and attempted to find correlation between the evolution of Mediator complex and its disorder. Our analysis suggests that disorder in Mediator complex have played a crucial role in the evolutionary diversification of complexity of eukaryotic organisms. Conserved intrinsic disordered regions (IDRs) were identified in only six subunits in the three kingdoms whereas unique patterns of IDRs were identified in other Mediator subunits. Acquisition of novel molecular recognition features (MoRFs) through evolution of new subunits or through elongation of the existing subunits was evident in metazoans and plants. A new concept of ‘junction-MoRF’ has been introduced. Evolutionary link between CBP and Med15 has been provided which explain the evolution of extended-IDR in CBP from Med15 KIX-IDR junction-MoRF suggesting role of junction-MoRF in evolution and modulation of protein–protein interaction repertoire. This study can be informative and helpful in understanding the conserved and flexible nature of Mediator complex across eukaryotic kingdoms.

The Mediator complex of Caenorhabditis elegans: insights into the developmental and physiological roles of a conserved transcriptional coregulator

The Mediator multiprotein complex (‘Mediator’) is an important transcriptional coregulator that is evolutionarily conserved throughout eukaryotes. Although some Mediator subunits are essential for the transcription of all protein-coding genes, others influence the expression of only subsets of genes and participate selectively in cellular signaling pathways. Here, we review the current knowledge of Mediator subunit function in the nematode Caenorhabditis elegans, a metazoan in which established and emerging genetic technologies facilitate the study of developmental and physiological regulation in vivo. In this nematode, unbiased genetic screens have revealed critical roles for Mediator components in core developmental pathways such as epidermal growth factor (EGF) and Wnt/β-catenin signaling. More recently, important roles for C. elegans Mediator subunits have emerged in the regulation of lipid metabolism and of systemic stress responses, engaging conserved transcription factors such as nuclear hormone receptors (NHRs). We emphasize instances where similar functions for individual Mediator subunits exist in mammals, highlighting parallels between Mediator subunit action in nematode development and in human cancer biology. We also discuss a parallel between the association of the Mediator subunit MED12 with several human disorders and the role of its C. elegans ortholog mdt-12 as a regulatory hub that interacts with numerous signaling pathways.

Functional studies of the yeast med5, med15 and med16 mediator tail subunits

The yeast Mediator complex can be divided into three modules, designated Head, Middle and Tail. Tail comprises the Med2, Med3, Med5, Med15 and Med16 protein subunits, which are all encoded by genes that are individually non-essential for viability. In cells lacking Med16, Tail is displaced from Head and Middle. However, inactivation of MED5/MED15 and MED15/MED16 are synthetically lethal, indicating that Tail performs essential functions as a separate complex even when it is not bound to Middle and Head. We have used the N-Degron method to create temperature-sensitive (ts) mutants in the Mediator tail subunits Med5, Med15 and Med16 to study the immediate effects on global gene expression when each subunit is individually inactivated, and when Med5/15 or Med15/16 are inactivated together. We identify 25 genes in each double mutant that show a significant change in expression when compared to the corresponding single mutants and to the wild type strain. Importantly, 13 of the 25 identified genes are common for both double mutants. We also find that all strains in which MED15 is inactivated show down-regulation of genes that have been identified as targets for the Ace2 transcriptional activator protein, which is important for progression through the G1 phase of the cell cycle. Supporting this observation, we demonstrate that loss of Med15 leads to a G1 arrest phenotype. Collectively, these findings provide insight into the function of the Mediator Tail module.

The C. elegans CDK8 Mediator module regulates axon guidance decisions in the ventral nerve cord and during dorsal axon navigation

Receptors expressed on the growth cone of outgrowing axons detect cues required for proper navigation. The pathway choices available to an axon are in part defined by the set of guidance receptors present on the growth cone. Regulated expression of receptors and genes controlling the localization and activity of receptors ensures that axons respond only to guidance cues relevant for reaching their targets. In genetic screens for axon guidance mutants, we isolated an allele of let-19/mdt-13, a component of the Mediator, a large ~30 subunit protein complex essential for gene transcription by RNA polymerase II. LET-19/MDT-13 is part of the CDK8 module of the Mediator. By testing other Mediator components, we found that all subunits of the CDK8 module as well as some other Mediator components are required for specific axon navigation decisions in a subset of neurons. Expression profiling demonstrated that let-19/mdt-13 regulates the expression of a large number of genes in interneurons. A mutation in the sax-3 gene, encoding a receptor for the repulsive guidance cue SLT-1, suppresses the commissure navigation defects found in cdk-8 mutants. This suggests that the CDK8 module specifically represses the SAX-3/ROBO pathway to ensure proper commissure navigation.

Phosphatase activity in barley proteins tightly bound to DNA and its development-dependent changes

The tightly bound proteins (TBPs), a protein group that remains attached to DNA either covalently or noncovalently after deproteinization, have been found in numerous eukaryotic species. Some TBPs isolated from mammalian and yeast cells possess phosphatase or kinase activity. The aim of this study was to characterize further TBPs in barley (Hordeum vulgare) cells. The spectra of TBPs varied in different organs of barley shoots (first leaves, coleoptile, and roots) and at different developmental stages of the plant. Some barley TBPs manifested phosphatase, probably Ser/Thr or dual Ser/Thr/Tyr activity. MALDI-TOF mass spectrometry of barley TBPs identified several proteins involved in chromatin rearrangement and regulation processes, including transcription factors, serpins, protein phosphatases and protein kinases, RNA helicases, and DNA topoisomerase II.

The Mediator complex in thyroid hormone receptor action

BACKGROUND

Mediator is an evolutionarily conserved multisubunit complex that plays an essential regulatory role in eukaryotic transcription of protein-encoding genes. The human complex was first isolated as a transcriptional coactivator bound to the thyroid hormone receptor (TR) and has since been shown to play a key coregulatory role for a broad range of nuclear hormone receptors (NRs) as well as other signal-activated transcription factors.

SCOPE OF REVIEW

We provide a general overview of Mediator structure and function, summarize the mechanisms by which Mediator is targeted to NRs, and outline recent evidence revealing Mediator as a regulatory axis for other distinct coregulatory factors, chromatin modifying enzymes and cellular signal transduction pathways.

MAJOR CONCLUSIONS

Besides serving as a functional interface with the RNA polymerase II basal transcription machinery, Mediator plays a more versatile role in regulating transcription including the ability to: a) facilitate gene-specific chromatin looping events; b) coordinate chromatin modification events with preinitiation complex assembly; and c) regulate critical steps that occur during transcriptional elongation. The variably associated MED1 subunit continues to emerge as a pivotal player in Mediator function, not only as the primary interaction site for NRs, but also as a crucial interaction hub for other coregulatory factors, and as an important regulatory target for signal-activated kinases.

GENERAL SIGNIFICANCE

Mediator plays an integral coregulatory role at NR target genes by functionally interacting with the basal transcription apparatus and by coordinating the action of chromatin modifying enzymes and transcription elongation factors. This article is part of a Special Issue entitled Thyroid hormone signalling.

The Mediator complex in plants: structure, phylogeny, and expression profiling of representative genes in a dicot (Arabidopsis) and a monocot (rice) during reproduction and abiotic stress

The Mediator (Med) complex relays regulatory information from DNA-bound transcription factors to the RNA polymerase II in eukaryotes. This macromolecular unit is composed of three core subcomplexes in addition to a separable kinase module. In this study, conservation of Meds has been investigated in 16 plant species representing seven diverse groups across the plant kingdom. Using Hidden Markov Model-based conserved motif searches, we have identified all the known yeast/metazoan Med components in one or more plant groups, including the Med26 subunits, which have not been reported so far for any plant species. We also detected orthologs for the Arabidopsis (Arabidopsis thaliana) Med32, -33, -34, -35, -36, and -37 in all the plant groups, and in silico analysis identified the Med32 and Med33 subunits as apparent orthologs of yeast/metazoan Med2/29 and Med5/24, respectively. Consequently, the plant Med complex appears to be composed of one or more members of 34 subunits, as opposed to 25 and 30 members in yeast and metazoans, respectively. Despite low similarity in primary Med sequences between the plants and their fungal/metazoan partners, secondary structure modeling of these proteins revealed a remarkable similarity between them, supporting the conservation of Med organization across kingdoms. Phylogenetic analysis between plant, human, and yeast revealed single clade relatedness for 29 Med genes families in plants, plant Meds being closer to human than to yeast counterparts. Expression profiling of rice (Oryza sativa) and Arabidopsis Med genes reveals that Meds not only act as a basal regulator of gene expression but may also have specific roles in plant development and under abiotic stress conditions.

Interactions between subunits of the Mediator complex with gene-specific transcription factors

The Mediator complex forms the bridge between gene-specific transcription factors and the RNA polymerase II (RNAP II) machinery. Mediator is a large polypetide complex consisting of about thirty polypeptides that are mostly conserved from yeast to human. Mediator coordinates RNAP II recruitment, phosphorylation of the C-terminal domain of RNAP II, enhancer-loop formation and post-initiation events. The focus of the review is to summarize the current knowledge of transcription factor/Mediator interactions in higher eukaryotes and illuminate the physiological and gene-selective roles of Mediator.

Recent advances in understanding the molecular mechanisms regulating C. elegans transcription

We review recent studies that have advanced our understanding of the molecular mechanisms regulating transcription in the nematode C. elegans. Topics covered include: (i) general properties of C. elegans promoters; (ii) transcription factors and transcription factor combinations involved in cell fate specification and cell differentiation; (iii) new roles for general transcription factors; (iv) nucleosome positioning in C. elegans "chromatin"; and (v) some characteristics of histone variants and histone modifications and their possible roles in controlling C. elegans transcription.

Identification of genes affecting wing patterning through a loss-of-function mutagenesis screen and characterization of med15 function during wing development

The development of the Drosophila melanogaster wing depends on the correct regulation of cell survival, growth, proliferation, differentiation, and pattern formation. These processes, and the genes controlling then, are common to the development of epithelia in many different organisms. To identify additional genes contributing to wing development we have carried out a genetic screen in mosaic wings carrying clones of homozygous mutant cells. We obtained 12 complementation groups corresponding to genes with a proven role in wing formation such as smoothened, thick veins, mothers against dpp, expanded, and fat and 71 new complementation groups affecting the pattern of veins and the size of wing. We mapped one of these groups to the mediator15 gene (med15), a component of the Mediator complex. We show that Med15 and other members of the Mediator complex are required, among other processes, for the transcription of decapentaplegic target genes.

Med8, Med18, and Med20 subunits of the Mediator head domain are interdependent upon each other for folding and complex formation

We have studied folding and complex formation of the yeast Mediator head-module protein subunits Med8, Med18, and Med20. Using a combination of immunoprecipitation, far-UV circular dichroism, and fluorescence measurements on recombinantly expressed and denatured proteins that were allowed to renature separately or in different combinations, we found that Med8, Med18, and Med20 can fold in different ways to form both soluble monomeric proteins and different distinct subcomplexes. However, the concurrent presence of all three protein subunits during the renaturation process is required for proper folding and trimer complex formation.

Comparative genomics supports a deep evolutionary origin for the large, four-module transcriptional mediator complex

The multisubunit Mediator (MED) complex bridges DNA-bound transcriptional regulators to the RNA polymerase II (PolII) initiation machinery. In yeast, the 25 MED subunits are distributed within three core subcomplexes and a separable kinase module composed of Med12, Med13 and the Cdk8-CycC pair thought to control the reversible interaction between MED and PolII by phosphorylating repeated heptapeptides within the Rpb1 carboxyl-terminal domain (CTD). Here, MED conservation has been investigated across the eukaryotic kingdom. Saccharomyces cerevisiae Med2, Med3/Pgd1 and Med5/Nut1 subunits are apparent homologs of metazoan Med29/Intersex, Med27/Crsp34 and Med24/Trap100, respectively, and these and other 30 identified human MED subunits have detectable counterparts in the amoeba Dictyostelium discoideum, indicating that none is specific to metazoans. Indeed, animal/fungal subunits are also conserved in plants, green and red algae, entamoebids, oomycetes, diatoms, apicomplexans, ciliates and the 'deep-branching' protists Trichomonas vaginalis and Giardia lamblia. Surprisingly, although lacking CTD heptads, T. vaginalis displays 44 MED subunit homologs, including several CycC, Med12 and Med13 paralogs. Such observations have allowed the identification of a conserved 17-subunit framework around which peripheral subunits may be assembled, and support a very ancient eukaryotic origin for a large, four-module MED. The implications of this comprehensive work for MED structure-function relationships are discussed.

The Mediator subunit MDT-15 confers metabolic adaptation to ingested material

In eukaryotes, RNA polymerase II (Pol_II) dependent gene expression requires accessory factors termed transcriptional coregulators. One coregulator that universally contributes to Pol_II-dependent transcription is the Mediator, a multisubunit complex that is targeted by many transcriptional regulatory factors. For example, the Caenorhabditis elegans Mediator subunit MDT-15 confers the regulatory actions of the sterol response element binding protein SBP-1 and the nuclear hormone receptor NHR-49 on fatty acid metabolism. Here, we demonstrate that MDT-15 displays a broader spectrum of activities, and that it integrates metabolic responses to materials ingested by C. elegans. Depletion of MDT-15 protein or mutation of the mdt-15 gene abrogated induction of specific detoxification genes in response to certain xenobiotics or heavy metals, rendering these animals hypersensitive to toxin exposure. Intriguingly, MDT-15 appeared to selectively affect stress responses related to ingestion, as MDT-15 functional defects did not abrogate other stress responses, e.g., thermotolerance. Together with our previous finding that MDT-15:NHR-49 regulatory complexes coordinate a sector of the fasting response, we propose a model whereby MDT-15 integrates several transcriptional regulatory pathways to monitor both the availability and quality of ingested materials, including nutrients and xenobiotic compounds.

All organisms adapt their physiology to external input, such as altered food availability or toxic challenges. Many of these responses are driven by changes in gene transcription. In general, sequence specific DNA-binding regulatory factors are considered the specificity determinants of the transcriptional output. Here, we show that, in the roundworm Caenorhabditis elegans, one subunit of a >20 subunit, evolutionarily conserved, non-DNA binding co-factor termed Mediator, specifies a portion of the metabolic responses to a mixture of ingested material. This protein, MDT-15, is required for appropriate expression of genes that protect worms from the effects of toxic compounds and heavy metals. Our previous findings showed that the same protein also cooperates with other regulators to coordinate lipid metabolism. We suggest that MDT-15 may “route” transcriptional responses appropriate to the ingested material. This physiological scope appears broader and more sophisticated than that of any individual regulatory factor, thus coordinating systemic metabolic adaptation with ingestion. Given the evolutionary conservation of MDT-15 and the Mediator, a similar regulatory pathway may ensure health and longevity in mammals.

Depletion of Med10 enhances Wnt and suppresses Nodal signaling during zebrafish embryogenesis

The transcriptional Mediator (MED) is a multiprotein complex that transmits information from transcription factors to RNA polymerase II (PolII) to regulate transcription. At present, the role of distinct MED subunits in general transcription versus transcription stimulated by specific signaling pathways is unclear. By means of positional cloning, we reveal that the zebrafish mutant tennismatch is a hypomorphic allele of Med10, a conserved MED middle domain subunit. Using morpholino antisense oligonucleotides, we further demonstrate that reduction of Med10 levels led to an enhancement of the Wnt signaling pathway, while also suggesting a role for Med10 in mediating the Nodal signaling pathway. In contrast to the dual roles of Med10, reduction of Med12 and Med13 levels, two MED subunits in the regulatory domain, led to an enhancement of the Wnt signaling pathway but not the Nodal pathway, while reduction of Med15 levels, a MED subunit in the tail domain, suppressed the Nodal signaling pathway but not the Wnt signaling pathway. Thus, Med10 appears to be a unique MED subunit that differentially transduces information from distinct signaling pathways during zebrafish embryogenesis.

Role of the mediator complex in nuclear hormone receptor signaling

Mediator is an evolutionarily conserved multisubunit protein complex that plays a key role in regulating transcription by RNA polymerase II. The complex functions by serving as a molecular bridge between DNA-bound transcriptional activators and the basal transcription apparatus. In humans, Mediator was first characterized as a thyroid hormone receptor (TR)-associated protein (TRAP) complex that facilitates ligand-dependent transcriptional activation by TR. More recently, Mediator has been established as an essential coactivator for a broad range of nuclear hormone receptors (NRs) as well as several other types of gene-specific transcriptional activators. A single subunit of the complex, MED1/TRAP220, is required for direct ligand-dependent interactions with NRs. Mediator coactivates NR-regulated gene expression by facilitating the recruitment and activation of the RNA polymerase II-associated basal transcription apparatus. Importantly, Mediator acts in concert with other NR coactivators involved in chromatin remodeling to initiate transcription of NR target genes in a multistep manner. In this review, we summarize the functional role of Mediator in NR signaling pathways with an emphasis on the underlying molecular mechanisms by which the complex interacts with NRs and subsequently facilitates their action. We also focus on recent advances in our understanding of TRAP/Mediator's pathophysiological role in mammalian disease and development.

Genome-wide occupancy profile of mediator and the Srb8-11 module reveals interactions with coding regions

Mediator exists in a free form containing the Med12, Med13, CDK8, and CycC subunits (the Srb8-11 module) and a smaller form, which lacks these four subunits and associates with RNA polymerase II (Pol II), forming a holoenzyme. We use chromatin immunoprecipitation (ChIP) and DNA microarrays to investigate genome-wide localization of Mediator and the Srb8-11 module in fission yeast. Mediator and the Srb8-11 module display similar binding patterns, and interactions with promoters and upstream activating sequences correlate with increased transcription activity. Unexpectedly, Mediator also interacts with the downstream coding region of many genes. These interactions display a negative bias for positions closer to the 5' ends of open reading frames (ORFs) and appear functionally important, because downregulation of transcription in a temperature-sensitive med17 mutant strain correlates with increased Mediator occupancy in the coding region. We propose that Mediator coordinates transcription initiation with transcriptional events in the coding region of eukaryotic genes.

Interactions between subunits of Drosophila Mediator and activator proteins

Mediator was first identified because of its activity in activator-stimulated transcription in vivo and in vitro. Later, biochemical fractionation led to the co-purification of the multi-subunit Mediator complex and RNA polymerase II (pol II). Results of these studies suggested a model whereby transcription-activator proteins, which bind to specific gene regulatory sequences, recruit both Mediator and pol II as a holoenzyme in a one-step mechanism. More recent studies of Drosophila Mediator and additional studies in yeast have demonstrated that different transcription activators can bind and recruit Mediator to promoters in vivo in a step that is independent of pol II recruitment. Moreover, the different activators in Drosophila bind and recruit Mediator via physical interactions with specific subsets of proteins. These features of Mediator function seem to be broadly conserved.

Components of the transcriptional Mediator complex are required for asymmetric cell division inC. elegans

Asymmetric cell division is a fundamental process that produces cellular diversity during development. In C. elegans, the Wnt signaling pathway regulates the asymmetric divisions of a number of cells including the T blast cell. We found that the let-19 and dpy-22 mutants have defects in their T-cell lineage, and lineage analyses showed that the defects were caused by disruption in the asymmetry of the T-cell division. We found that let-19 and dpy-22 encode homologs of the human proteins MED13/TRAP240 and MED12/TRAP230, respectively, which are components of the Mediator complex. Mediator is a multi-component complex that can regulate transcription by transducing the signals between activators and RNA polymerase in vitro. We also showed that LET-19 and DPY-22 form a complex in vivo with other components of Mediator, SUR-2/MED23 and LET-425/MED6. In the let-19 and dpy-22 mutants, tlp-1, which is normally expressed asymmetrically between the T-cell daughters through the function of the Wnt pathway, was expressed symmetrically in both daughter cells. Furthermore, we found that the let-19 and dpy-22 mutants were defective in the fusion of the Pn.p cell, a process that is regulated by bar-1/β-catenin. Ectopic cell fusion in bar-1 mutants was suppressed by the let-19 or dpy-22 mutations, while defective cell fusion in let-19 mutants was suppressed by lin-39/Hox mutations, suggesting that let-19 and dpy-22 repress the transcription of lin-39. These results suggest that LET-19 and DPY-22 in the Mediator complex repress the transcription of Wnt target genes.

cDNA cloning and characterization of the human THRAP2 gene which maps to chromosome 12q24, and its mouse ortholog Thrap2

Characterization of a balanced t(2;12)(q37;q24) translocation in a patient with suspicion of Noonan syndrome revealed that the chromosome 12 breakpoint lies in the vicinity of a novel human gene, thyroid hormone receptor-associated protein 2 (THRAP2). We therefore characterized this gene and its mouse counterpart in more detail. Human and mouse THRAP2/Thrap2 span a genomic region of about 310 and >170 kilobases (kb), and both contain 31 exons. Corresponding transcripts are approximately 9.5 kb long. Their open reading frames code for proteins of 2210 and 2203 amino acids, which are 93% identical. By northern blot analysis, human and mouse THRAP2/Thrap2 genes showed ubiquitous expression. Transcripts were most abundant in human skeletal muscle and in mouse heart. THRAP2 protein is 56% identical to human TRAP240, which belongs to the thyroid hormone receptor associated protein (TRAP) complex and is evolutionary conserved up to yeast. This complex is involved in transcriptional regulation and is believed to serve as adapting interface between regulatory proteins bound to specific DNA sequences and RNA polymerase II.

Long lifespan in worms with long telomeric DNA

Telomere length is a crucial factor in senescence, but it has not been determined whether animals with long telomeres live longer than those with normal-length telomeres in the isogenic background of a given species. Here we show the effect of long telomeres on lifespan in the nematode Caenorhabditis elegans. We examined the effect of telomere length on lifespan by overexpressing HRP-1, a telomere-binding protein, which gradually increased telomere length in worms. Worms with longer telomeres lived longer. We confirmed that the extension of lifespan was due to the increased telomere length, and not to the overexpression of HRP-1 per se, by examining the lifespans of nontransgenic progeny of the transgenic worms, who retained the longer telomeres. The lifespan-extending effect of long telomeres was dependent on daf-16. The number of germ stem cells was not affected in worms with long telomeres, indicating that the telomere effect on lifespan is independent of germ stem cell cycling. Worms with long telomeres were more resistant to heat stress. Taken together, our results suggest that signaling may be initiated in postmitotic somatic cells by telomere length to regulate organismal lifespan.

The Caenorhabditis elegans ortholog of TRAP240, CeTRAP240/let-19, selectively modulates gene expression and is essential for embryogenesis

Mediator complexes are large multiprotein assemblies that function in the regulation of eukaryotic gene transcription. In yeast, certain mediator subunits appear to comprise a subcomplex that acts in the regulation of a specific subset of genes. We investigated in a metazoan, Caenorhabditis elegans, the roles and interactions of two of those subunits, CeTRAP240/let-19 and CeTRAP230/dpy-22. We found that CeTRAP240/let-19 contains four domains that are conserved in the human TRAP240 protein and that one of those domains displays intrinsic transcriptional repression activity. Using RNA interference, we found that reduced expression of CeTRAP240/let-19 displayed a high penetrance of embryonic lethality in F1 progeny; animals that escaped embryonic arrest showed mutant phenotypes such as burst vulva and molting defects. CeTRAP240/let-19 appeared to affect specific genes, as CeTRAP240/let-19(RNAi) led to selectively reduced expression of a subset of reporter genes examined. Genetic experiments supported the view that CeTRAP240/let-19 and CeTRAP230/dpy-22, like their Drosophila and yeast counterparts, can operate on common pathways. Thus, a male tail phenotype caused by the pal-1(e2091) mutation was suppressed not only by CeTRAP230/dpy-22 mutants, as reported previously, but also by reduced expression of CeTRAP240/let-19. Additionally, CeTRAP240/let-19(RNAi) in a CeTRAP230/dpy-22 mutant background produced a strong synthetic lethal phenotype. Overall, our results establish specific roles of CeTRAP240/let-19 in C. elegans embryonic development and a functional interaction between CeTRAP240/let-19 and CeTRAP230/dpy-22. Interestingly, whereas this interaction has been conserved from yeast to mammals, the subcomplex modulates metazoan-specific genetic pathways, likely in addition to those also controlled in yeast.

Identification of HMG-5 as a double-stranded telomeric DNA-binding protein in the nematode Caenorhabditis elegans

Many protein components of telomeres, the multifunctional DNA-protein complexes at the ends of eukaryotic chromosomes, have been identified in diverse species ranging from yeast to humans. In Caenorhabditis elegans, CEH-37 has been identified by a yeast one hybrid screen to be a double-stranded telomere-binding protein. However, the role of CEH-37 in telomere function is unclear because a deletion mutation in this gene does not cause severe telomere defects. This observation raises the possibility of the presence of genetic redundancy. To identify additional double-stranded telomere-binding proteins in C. elegans, we used a different approach, namely, a proteomic approach. Affinity chromatography followed by Finnigan LCQ ion trap mass spectrometer analysis allowed us to identify several candidate proteins. We further characterized one of these, HMG-5, which is encoded by F45E4.9. HMG-5 bound to double-stranded telomere in vitro as shown by competition assays. At least two telomeric DNA repeats were needed for this binding. HMG-5 was expressed in the nuclei of the oocytes and all embryonic cells, but not in the hatched larvae or adults. HMG-5 mainly localized to the chromosomal ends, indicating that HMG-5 also binds to telomeres in vivo. These observations suggest that HMG-5 may participate, together with CEH-37, in early embryogenesis by acting at the telomeres.

The mediator coactivator complex: functional and physical roles in transcriptional regulation

In vivo, the DNA is packed into chromatin and transcription is dependent upon activators that recruit other factors to reverse the repressive effects of chromatin. The response to activators requires additional factors referred to as coactivators. One such coactivator, mediator, is a multi-subunit complex capable of responding to different activators. It plays an key role in activation, bridging DNA-bound activators, the general transcriptional machinery, especially RNA polymerase II, and the core promoter. Its subunits are necessary for a variety of positive and negative regulatory processes and serve as the direct targets of activators themselves. In vivo and in vitro studies support various roles for mediator in transcription initiation, while structural studies demonstrate that it engages in multiple interactions with RNA polymerase II, and adopts conformations that are activator specific.

Human mediator enhances activator-facilitated recruitment of RNA polymerase II and promoter recognition by TATA-binding protein (TBP) independently of TBP-associated factors

Mediator is a general cofactor implicated in the functions of many transcriptional activators. Although Mediator with different protein compositions has been isolated, it remains unclear how Mediator facilitates activator-dependent transcription, independent of its general stimulation of basal transcription. To define the mechanisms of Mediator function, we isolated two forms of human Mediator complexes (Mediator-P.5 and Mediator-P.85) and demonstrated that Mediator-P.5 clearly functions by enhancing activator-mediated recruitment of RNA polymerase II (pol II), whereas Mediator-P.85 works mainly by stimulating overall basal transcription. The coactivator function of Mediator-P.5 was not impaired when TATA-binding protein (TBP) was used in place of TFIID, but it was abolished when another general cofactor, PC4, was omitted from the reaction or when Mediator-P.5 was added after pol II entry into the preinitiation complex. Moreover, Mediator- P.5 is able to enhance TBP binding to the TATA box in an activator-dependent manner. Our data provides biochemical evidence that Mediator functions by facilitating activator-mediated recruitment of pol II and also promoter recognition by TBP, both of which can occur in the absence of TBP-associated factors in TFIID.

Two subunits of the Drosophila mediator complex act together to control cell affinity

The organizing centers for Drosophila imaginal disc development are created at straight boundaries between compartments; these are maintained by differences in cell affinity controlled by selector genes and intercellular signals. skuld and kohtalo encode homologs of TRAP240 and TRAP230, the two largest subunits of the Drosophila mediator complex; mutations in either gene cause identical phenotypes. We show here that both genes are required to establish normal cell affinity differences at the anterior-posterior and dorsal-ventral compartment boundaries of the wing disc. Mutant cells cross from the anterior to the posterior compartment, and can distort the dorsal-ventral boundary in either the dorsal or ventral direction. The Skuld and Kohtalo proteins physically interact in vivo and have synergistic effects when overexpressed, consistent with a skuld kohtalo double-mutant phenotype that is indistinguishable from either single mutant. We suggest that these two subunits do not participate in all of the activities of the mediator complex, but form a submodule that is required to regulate specific target genes, including those that control cell affinity.

A component of the transcriptional mediator complex inhibits RAS-dependent vulval fate specification in C. elegans

Negative regulation of receptor tyrosine kinase (RTK)/RAS signaling pathways is important for normal development and the prevention of disease in humans. We have used a genetic screen in C. elegans to identify genes that antagonize the activity of activated LET-23, a member of the EGFR family of RTKs. We identified two loss-of-function mutations in dpy-22, previously cloned as sop-1, that promote the ability of activated LET-23 to induce ectopic vulval fates. DPY-22 is a glutamine-rich protein that is most similar to human TRAP230, a component of a transcriptional mediator complex. DPY-22 has previously been shown to regulate WNT responses through inhibition of the beta-catenin-like protein BAR-1. We provide evidence that DPY-22 also inhibits RAS-dependent vulval fate specification independently of BAR-1, and probably regulates the activities of multiple transcription factors during development. Furthermore, we demonstrate that although inhibition of BAR-1-dependent gene expression has been shown to require the C-terminal glutamine-rich region, this region is dispensable for inhibition of RAS-dependent cell differentiation. Thus, the glutamine-rich region contributes to specificity of this class of mediator protein.

Broad requirement for the mediator subunit RGR-1 for transcription in the Caenorhabditis elegans embryo

The Mediator-related transcription co-factors integrate positive and negative inputs and recruit and activate the RNA polymerase II complex. To understand the role of Mediator during transcription, it is important to identify Mediator subunits that are essential for its functions. In the yeast Mediator, the conserved component Rgr1 is associated with multiple subunits that are required for specific activation or repression events. Yeast rgr1 is essential for viability, for certain repression mechanisms, and for activation of heat shock genes, but it is not known whether rgr1 is generally important for transcription. Here we have performed the first analysis of rgr-1 function in a metazoan. We found that in the developing Caenorhabditis elegans embryo rgr-1 is broadly required for transcription and for phosphorylation of both Ser-2 and Ser-5 of the RNA polymerase II C-terminal domain repeat. We conclude that RGR-1 fulfills a critical Mediator function that is broadly essential for metazoan mRNA transcription and that RGR-1 may be required at an early recruitment or initiation step.

Evidence for a mediator of RNA polymerase II transcriptional regulation conserved from yeast to man

Mediator complexes (MED) link transcriptional regulators to RNA polymerase II. Here, we summarize the latest advances on the functional organization of yeast Mediator. We argue for the existence of a "universal" Mediator structurally conserved from yeast to man, based on an extensive analysis of sequence databases. Finally, we examine the implications of these observations for the physiological roles of metazoan MED subunits.

Identification of Schizosaccharomyces pombe genes that encode putative homologues of Saccharomyces cerevisiae mediator complex subunits

The mediator complexes transduce regulatory information from upstream regulatory elements to the transcription machinery in organisms ranging from yeasts to humans. By a genome-wide search we identified 14 ORFs and genes in the genome of the fission yeast Schizosaccharomyces pombe that encode putative homologues of Saccharomyces cerevisiae mediator subunits. The Sch. pombe proteins are smaller and appear to form a mediator of lower complexity, which is consistent with the hypothesized ancient origin of fission yeasts.

The MED-7 transcriptional mediator encoded by let-49 is required for gonad and germ cell development in Caenorhabditis elegans

Transcription mediators are evolutionarily conserved from yeast to human. We previously reported the specific in vivo roles of mediators during development. Transcriptional mediators including med-6, med-7, and med-10 were shown to be involved in the regulated transcription of specific genes, but not in the transcription of ubiquitous genes. In this report we have identified and characterized the Caenorhabditis elegans med-7 gene. A genetic mutation in the med-7 gene was identified by comparing genetic and physical maps and determining the molecular lesion. let-49 was found to have a nonsense mutation in the coding region of the med-7 gene. The identification of let-49 as the med-7 gene was confirmed by rescue experiments. The phenotype of the let-49 mutation indicated that the med-7 gene is required for normal postembryonic development. RNAi experiments showed that med-7 is also involved in embryogenesis and the gonad and germ cell development.

Analysis of Schizosaccharomyces pombe mediator reveals a set of essential subunits conserved between yeast and metazoan cells

With the identification of eight new polypeptides, we here complete the subunit characterization of the Schizosaccharomyces pombe RNA polymerase II holoenzyme. The complex contains homologs to all 10 essential gene products present in the Saccharomyces cerevisiae Mediator, but lacks clear homologs to any of the 10 S. cerevisiae components encoded by nonessential genes. S. pombe Mediator instead contains three unique components (Pmc2, -3, and -6), which lack homologs in other cell types. Presently, pmc2(+) and pmc3(+) have been shown to be nonessential genes. The data suggest that S. pombe and S. cerevisiae share an essential protein module, which associates with nonessential speciesspecific subunits. In support of this view, sequence analysis of the conserved yeast Mediator components Med4 and Med8 reveals sequence homology to the metazoan Mediator components Trap36 and Arc32. Therefore, 8 of 10 essential genes conserved between S. pombe and S. cerevisiae also have a metazoan homolog, indicating that an evolutionary conserved Mediator core is present in all eukaryotic cells. Our data suggest a closer functional relationship between yeast and metazoan Mediator than previously anticipated.

Med9/Cse2 and Gal11 modules are required for transcriptional repression of distinct group of genes

The yeast Mediator is composed of two subcomplexes, Rgr1 and Srb4, known to be required for diverse aspects of transcriptional regulation; however, their structural and functional organizations have not yet been deciphered in detail. Biochemical analyses designed to determine the subunit composition of the Rgr1 subcomplex revealed that the regulator-interacting subcomplex has a modular structure and is composed of the Gal11, Med9/Cse2, and Med10/Nut2 modules. Genome-wide gene expression and Northern analyses performed in the presence or absence of the various Mediator modules revealed a distinct requirement for the Gal11, Med9/Cse2, and Med10/Nut2 modules in transcriptional repression as well as activation. GST pull-down analysis revealed that the transcriptional repressor Tup1 binds to distinct but overlapping regions of the Gal11 module that were shown previously to be transcriptional activator binding sites. These data suggest that competition between transcriptional activators and repressors for a common binding site in the Mediator and distinct conformational changes in the Mediator induced by repressor binding may underlie the mechanism of transcriptional repression in eukaryotes.

A single-stranded telomere binding protein in the nematode Caenorhabditis elegans

We identified and characterized a protein (STB-1) from the nuclear extract of Caenorhabditis elegans that specifically binds single-stranded telomere DNA sequences, but not the corresponding RNA sequences. STB-1 binding activity is specific to the nematode telomere, but not to the human or plant telomere. STB-1 requires the core nucleotides of GCTTAGG and three spacer nucleotides in front of them for binding. While any single nucleotide change in the core sequence abolishes binding, the spacer nucleotides tolerate substitution. STB-1 was determined to be a basic protein of 45 kDa by Southwestern analyses. STB-1 forms a stable complex with DNA once bound to the telomere.

Biological significance of a universally conserved transcription mediator in metazoan developmental signaling pathways

Transcription mediators are known to be required for regulated transcription in yeast and higher eukaryotes. However, little is known about the specific roles of mediators in vivo during development. In this report, we have characterized the biological functions of the C. elegans genemed-6, which is the homolog of the yeast mediator med-6. We first identified a genetic mutation in the med-6 gene by comparing genetic and physical maps and determining the molecular lesion. Next, we demonstrated that med-6 plays an important role in metazoan development by regulating the transcription of genes in evolutionarily conserved signaling pathways. We showed that med-6 is involved in the transcription of genes of the Ras pathway by showing that med-6 RNAi suppressed phenotypes associated with gain-of-function alleles oflet-23 and let-60, and enhanced those associated with a reduction-of-function allele of lin-3. We also found thatmed-6 is involved in male ray development, which is partly mediated by the Wnt pathway. As MED-6 is universally conserved, including in yeast, and the mediator-related proteins that function in vulval and male ray development are metazoan specific, our results suggest the role of med-6 as a point of convergence where signals transmitted through metazoan-specific mediator-related proteins meet. In addition, RNAi experiments inrde-1 background showed that maternal and zygotic med-6activities have distinct roles in development.

Drosophila Med6 is required for elevated expression of a large but distinct set of developmentally regulated genes

Mediator is the evolutionarily conserved coactivator required for the integration and recruitment of diverse regulatory signals to basal transcription machinery. To elucidate the functions of metazoan Mediator, we isolated Drosophila melanogaster Med6 mutants. dMed6 is essential for viability and/or proliferation of most cells. dMed6 mutants failed to pupate and died in the third larval instar with severe proliferation defects in imaginal discs and other larval mitotic cells. cDNA microarray, quantitative reverse transcription-PCR, and in situ expression analyses of developmentally regulated genes in dMed6 mutants showed that transcriptional activation of many, but not all, genes was affected. Among the genes found to be affected were some that play a role in cell proliferation and metabolism. Therefore, dMed6 is required in most cells for transcriptional regulation of many genes important for diverse aspects of Drosophila development.

Mediator complexes and transcription

Over the past decade, various components of the transcription machinery have been identified as potential targets for activators. Recently, metazoan versions of yeast Mediator have been isolated and found to act as key coactivators to many transcription factors. Recent work has defined the composition, function and biology of metazoan mediator complexes, which has led us to propose a new nomenclature for the variously named versions of the mediator complex.

The TRAP/SMCC/Mediator complex and thyroid hormone receptor function

The TRAP/SMCC/Mediator complex is a mammalian transcriptional regulatory complex that contains over 25 polypeptides and is, in part, phylogenetically conserved. It was originally isolated as a thyroid hormone receptor (TR)-associated protein (TRAP) complex that mediates TR-activated transcription from DNA templates in conjunction with the general transcription machinery, and probably acts in vivo after the action of other receptor-interacting coactivators involved in chromatin remodeling. Subsequently, the TRAP complex was identified as a more broadly used coactivator complex for a wide variety of activators. The TRAP220 subunit mediates ligand-dependent interactions of the complex with TR and other nuclear receptors; and genetic ablation of murine TRAP220 has revealed that it is essential both for optimal TR function and for a variety of early developmental and adult homeostasis events in mice, but not for cell viability per se.