Mediator Research Articles

Defining the essential function of FBP/KSRP proteins: Drosophila Psi interacts with the mediator complex to modulate MYC transcription and tissue growth.

Despite two decades of research, the major function of FBP-family KH domain proteins during animal development remains controversial. The literature is divided between RNA processing and transcriptional functions for these single stranded nucleic acid binding proteins. Using Drosophila, where the three mammalian FBP proteins (FBP1-3) are represented by one ortholog, Psi, we demonstrate the primary developmental role is control of cell and tissue growth. Co-IP-mass spectrometry positioned Psi in an interactome predominantly comprised of RNA Polymerase II (RNA Pol II) transcriptional machinery and we demonstrate Psi is a potent transcriptional activator. The most striking interaction was between Psi and the transcriptional mediator (MED) complex, a known sensor of signaling inputs. Moreover, genetic manipulation of MED activity modified Psi-dependent growth, which suggests Psi interacts with MED to integrate developmental growth signals. Our data suggest the key target of the Psi/MED network in controlling developmentally regulated tissue growth is the transcription factor MYC. As FBP1 has been implicated in controlling expression of the MYC oncogene, we predict interaction between MED and FBP1 might also have implications for cancer initiation and progression.

HSI2 Repressor Recruits MED13 and HDA6 to Down-Regulate Seed Maturation Gene Expression Directly During Arabidopsis Early Seedling Growth.

Arabidopsis HSI2 (HIGH-LEVEL EXPRESSION OF SUGAR-INDUCIBLE GENE 2) which carries a EAR (ERF-associated amphiphilic repression) motif acts as a repressor of seed maturation genes and lipid biosynthesis, whereas MEDIATOR (MED) is a conserved multiprotein complex linking DNA-bound transcription factors to RNA polymerase II transcription machinery. How HSI2 executes its repressive function through MED is hitherto unknown. Here, we show that HSI2 and its homolog, HSI2-lik (HSL1), are able to form homo- and heterocomplexes. Both factors bind to the TRAP240 domain of MED13, a subunit of the MED CDK8 module. Mutant alleles of the med13 mutant show elevated seed maturation gene expression and increased lipid accumulation in cotyledons; in contrast, HSI2- or MED13-overexpressing plants display the opposite phenotypes. The overexpression phenotypes of HSI2 and MED13 are abolished in med13 and hsi2 hsl1, respectively, indicating that HSI2 and MED13 together are required for these functions. The HSI2 C-terminal region interacts with HDA6, whose overexpression also reduces seed maturation gene expression and lipid accumulation. Moreover, HSI2, MED13 and HDA6 bind to the proximal promoter and 5'-coding regions of seed maturation genes. Taken together, our results suggest that HSI2 recruits MED13 and HDA6 to suppress directly a subset of seed maturation genes post-germination.

An Integrated Genomic Strategy Delineates Candidate Mediator Genes Regulating Grain Size and Weight in Rice.

The present study deployed a Mediator (MED) genes-mediated integrated genomic strategy for understanding the complex genetic architecture of grain size/weight quantitative trait in rice. The targeted multiplex amplicon resequencing of 55 MED genes annotated from whole rice genome in 384 accessions discovered 3971 SNPs, which were structurally and functionally annotated in diverse coding and non-coding sequence-components of genes. Association analysis, using the genotyping information of 3971 SNPs in a structured population of 384 accessions (with 50–100 kb linkage disequilibrium decay), detected 10 MED gene-derived SNPs significantly associated (46% combined phenotypic variation explained) with grain length, width and weight in rice. Of these, one strong grain weight-associated non-synonymous SNP (G/A)-carrying OsMED4_2 gene was validated successfully in low- and high-grain weight parental accessions and homozygous individuals of a rice mapping population. The seed-specific expression, including differential up/down-regulation of three grain size/weight-associated MED genes (including OsMED4_2) in six low and high-grain weight rice accessions was evident. Altogether, combinatorial genomic approach involving haplotype-based association analysis delineated diverse functionally relevant natural SNP-allelic variants in 10 MED genes, including three potential novel SNP haplotypes in an OsMED4_2 gene governing grain size/weight differentiation in rice. These molecular tags have potential to accelerate genomics-assisted crop improvement in rice.

Biochemical and redox characterization of the mediator complex and its associated transcription factor GeBPL, a GLABROUS1 enhancer binding protein.

The eukaryotic mediator integrates regulatory signals from promoter-bound transcription factors (TFs) and transmits them to RNA polymerase II (Pol II) machinery. Although redox signalling is important in adjusting plant metabolism and development, nothing is known about a possible redox regulation of mediator. In the present study, using pull-down and yeast two-hybrid assays, we demonstrate the association of mediator (MED) subunits MED10a, MED28 and MED32 with the GLABROUS1 (GL1) enhancer-binding protein-like (GeBPL), a plant-specific TF that binds a promoter containing cryptochrome 1 response element 2 (CryR2) element. All the corresponding recombinant proteins form various typesof covalent oligomers linked by intermolecular disulfide bonds that are reduced invitro by the thioredoxin (TRX) and/or glutathione/glutaredoxin (GRX) systems. The presence of recombinant MED10a, MED28 and MED32 subunits or changes of its redox state affect the DNA-binding capacity of GeBPL suggesting that redox-driven conformational changes might modulate its activity. Overall, these results advance our understanding of how redox signalling affects transcription and identify mediator as a novel actor in redox signalling pathways, relaying or integrating redox changes in combination with specific TFs as GeBPL.

RNA-Seq for the identification of novel Mediator transcripts in endothelial progenitor cells.

Mediator (MED) complex is a multiprotein playing a key role in the eukaryotic transcription. Alteration of MED function may have enormous pathophysiological consequences and several MED genes have been implicated in human diseases. Here, we have combined computational and experimental approaches to identify and characterize, new transcripts generated by alternative splicing (AS) for all MED genes, through the analysis of our recently published RNA-Sequencing datasets of endothelial progenitor cells (EPCs). This combined strategy allowed us to identify novel transcripts for MED4, MED9, MED11, MED14, MED27 and CDK8 most of them generated by AS. All the newly identified transcripts, except MED11, are predicted to encode novel protein isoforms. The identification of novel MED variants could lead to the finding of other MED complexes with different functions depending on their subunit composition. Finally, the expression profile of all MED genes, together with an extensive gene expression analysis, may be useful to better classify the diverse subsets of cell populations that contribute to neovascularization.

Drosophila melanogaster Hox transcription factors access the RNA polymerase II machinery through direct homeodomain binding to a conserved motif of mediator subunit Med19.

Hox genes in species across the metazoa encode transcription factors (TFs) containing highly-conserved homeodomains that bind target DNA sequences to regulate batteries of developmental target genes. DNA-bound Hox proteins, together with other TF partners, induce an appropriate transcriptional response by RNA Polymerase II (PolII) and its associated general transcription factors. How the evolutionarily conserved Hox TFs interface with this general machinery to generate finely regulated transcriptional responses remains obscure. One major component of the PolII machinery, the Mediator (MED) transcription complex, is composed of roughly 30 protein subunits organized in modules that bridge the PolII enzyme to DNA-bound TFs. Here, we investigate the physical and functional interplay between Drosophila melanogaster Hox developmental TFs and MED complex proteins. We find that the Med19 subunit directly binds Hox homeodomains, in vitro and in vivo. Loss-of-function Med19 mutations act as dose-sensitive genetic modifiers that synergistically modulate Hox-directed developmental outcomes. Using clonal analysis, we identify a role for Med19 in Hox-dependent target gene activation. We identify a conserved, animal-specific motif that is required for Med19 homeodomain binding, and for activation of a specific Ultrabithorax target. These results provide the first direct molecular link between Hox homeodomain proteins and the general PolII machinery. They support a role for Med19 as a PolII holoenzyme-embedded “co-factor” that acts together with Hox proteins through their homeodomains in regulated developmental transcription.

CAUSES OF DELAY IN INDIAN TRANSPORTATION INFRASTRUCTURE PROJECTS

A survey on time performance of different types of construction projects in western Maharashtra was co nducted to determine the causes of delay and their importance according to e ach of the project participants, i.e., the owner, consultant and the contractor. Sixty four causes of delay were identified during the res earch. It seems that the problem is common and nota ble as 72% of the total infrastructure projects reported by all the respond ents were delivered late, whereas only 28% were com pleted on time. Clients’ respondents indicated that 59% of the public projec ts they were involved in were delivered late. Consu ltants’ respondents reported that 62% of the projects they were involved in were completed late. Contractors’ respondents also shar e the same view and articulated that 77% of the projects they are invol ved in exceeded the preset duration. The top five icauses of construction delays in transportation infrastructure projects ar e mainly Land Acquisition, Environmental Impact of the project, financial closure, Change orders by the client, Poor site management asupervision by contractor .Respondent’s opinion about the contribution towards the delay is 50 % respondent feels that del ay in the construction in mainly due to the contrac tor. 40 % of respondent feel that client is mainly responsible for the delay in const ruction projects. And only 10 % of respondent feel that delay mainly occur due to consultant. It is evident that consultant as a medi ator has less responsibility in construction delays .

185-P: IDENTIFICATION BY RNA-Seq OF NOVEL ANCESTRAL MEDIATOR TRANSCRIPTS IN ENDOTHELIAL PROGENITORS

Aim Mediator (MED) complex functions as a pivotal adaptor between transcription factors bounded at gene regulatory elements, RNA polymerase II and general transcription factors. Different ancestral humanMED complexes including at least 30 distinct MED subunits (MEDs) have been isolated. Because of the importance of ancestral MED role in the transcription of the eukaryotic genes, disruption of MED function may have relevant pathophysiological consequence also in the cardiovascular system and transplantation. Here, we have analyzed the expression data relative to MEDs in human endothelial progenitor cells (EPCs) obtained by RNA-Seq on a next generation sequencing platform. The introduction of next generation sequencing (NGS) technologies has revealed the complexity of mammalian transcriptomes, enabling to effectively explore, with an unprecedented throughput capacity, simple and complex genomes and even their differences in health and disease conditions. Methods RNA was isolated from early human EPCs and after ribodepletion it was used for the RNA-Seq through SOLID System. Results By analysis of RNA-Seq data and RT-PCR validation we have identified novel transcripts in several MED genes (including MED1, MED 15, MED 17 and MED23). Some of these transcripts are different in their 5’ and 3’ UTRs. Other transcripts are differently spliced thus excluding or including known/new exons. Conclusions This findings contribute to the characterization of novel MED transcripts in EPCs that could participate to the regulation of genes involved in different cell states. Our findings could have relevant implications in the regenerative action of EPCs in the cardiovascular system immune response after cardiac transplantation.

Many Paths to Alopecia via Compromised Regeneration of Hair Follicle Stem Cells

Alopecia can be caused by defective formation, defective regeneration, or increased destruction of hair follicles. Much work has elucidated the roles of diffusible morphogens in modulating hair follicle stem cell activities. Recent studies have revealed novel molecular events within the nucleus, which are required for the activation and progression of hair stem cells. These studies will provide new clues and targets for designing therapeutic strategies for hair loss.

Distinct alternative splicing patterns of mediator subunit genes during endothelial progenitor cell differentiation

Mediator (MED) is a fundamental component of the RNA polymerase II-mediated transcription machinery playing a pivotal role in the regulation of eukaryotic mRNA synthesis. Human MED complexes contain at least 30 distinct MED subunits. Our previous study, aimed to analyse MED complex during the pattern of endothelial progenitor cells (EPCs) differentiation, found an alternative transcript of MED30 subunit expressed only in circulating immature progenitor cells. Here, we report two novel transcripts of MED12 and MED19 subunits both generated by alternative splicing and displaying similar expression patterns, thereby indicating their involvement during endothelial cell differentiation.

Coactivator MED1 Ablation in Keratinocytes Results in Hair-Cycling Defects and Epidermal Alterations

The transcriptional coactivator complex Mediator facilitates transcription of nuclear hormone receptors and other transcription factors. We have previously isolated the Mediator complex from primary keratinocytes as the vitamin D receptor interacting protein complex. We identified a role for Mediator in keratinocyte proliferation and differentiation in cultured keratinocytes. Here, we investigated the in vivo role of Mediator by generating conditional null mice, where a critical subunit of the Mediator complex, MED1, is deleted from their keratinocytes. The MED1 ablation resulted in aberrant hair differentiation and cycling leading to hair loss. During the first hair follicle cycle, MED1 deletion resulted in a rapid regression of the hair follicles. Hair differentiation was reduced, and β-catenin/vitamin D receptor (VDR) regulated gene expression was dramatically decreased. In the subsequent adult hair cycle, MED1 ablation activated the initiation of hair follicle cycling. Shh signaling was increased, but terminal differentiation was not sufficient. Deletion of MED1 also caused hyper-proliferation of interfollicular epidermal keratinocytes, and increased the expression of epidermal differentiation markers. These results indicate that MED1 plays a critical role in regulating hair/epidermal proliferation and differentiation.

Distinct roles for Mediator Cdk8 module subunits in Drosophila development

Mediator (MED) is a conserved multisubunit complex bridging transcriptional activators and repressors to the general RNA polymerase II initiation machinery. In yeast, MED is organized in three core modules and a separable 'Cdk8 module' consisting of the cyclin-dependent kinase Cdk8, its partner CycC, Med12 and Med13. This regulatory module, specifically required for cellular adaptation to environmental cues, is thought to act through the Cdk8 kinase activity. Here we have investigated the functions of the four Cdk8 module subunits in the metazoan model Drosophila. Physical interactions detected among the four fly subunits provide support for a structurally conserved Cdk8 module. We analyzed the in vivo functions of this module using null mutants for Cdk8, CycC, Med12 and Med13. Each gene is required for the viability of the organism but not of the cell. Cdk8-CycC and Med12-Med13 act as pairs, which share some functions but also have distinct roles in developmental gene regulation. These data reveal functional attributes of the Cdk8 module, apart from its regulated kinase activity, that may contribute to the diversification of genetic programs.

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.

Coactivator cross-talk specifies transcriptional output

Cells often fine-tune gene expression at the level of transcription to generate the appropriate response to a given environmental or developmental stimulus. Both positive and negative influences on gene expression must be balanced to produce the correct level of mRNA synthesis. To this end, the cell uses several classes of regulatory coactivator complexes including two central players, TFIID and Mediator (MED), in potentiating activated transcription. Both of these complexes integrate activator signals and convey them to the basal apparatus. Interestingly, many promoters require both regulatory complexes, although at first glance they may seem to be redundant. Here we have used RNA interference (RNAi) in Drosophila cells to selectively deplete subunits of the MED and TFIID complexes to dissect the contribution of each of these complexes in modulating activated transcription. We exploited the robust response of the metallothionein genes to heavy metal as a model for transcriptional activation by analyzing direct factor recruitment in both heterogeneous cell populations and at the single-cell level. Intriguingly, we find that MED and TFIID interact functionally to modulate transcriptional response to metal. The metal response element-binding transcription factor-1 (MTF-1) recruits TFIID, which then binds promoter DNA, setting up a "checkpoint complex" for the initiation of transcription that is subsequently activated upon recruitment of the MED complex. The appropriate expression level of the endogenous metallothionein genes is achieved only when the activities of these two coactivators are balanced. Surprisingly, we find that the same activator (MTF-1) requires different coactivator subunits depending on the context of the core promoter. Finally, we find that the stability of multi-subunit coactivator complexes can be compromised by loss of a single subunit, underscoring the potential for combinatorial control of transcription activation.

EFFECTS OF MALATHION METABOLITES ON DEGRANULATION OF AND MEDIATOR RELEASE BY HUMAN AND RAT BASOPHILIC CELLS

In the present study, the effects of malathion and malathion derivatives on histamine and β-hexosaminidase release by RBL-1 cells, rat peritoneal mast cells (RPMC), and human peripheral blood basophils (HPBB) and cutaneous mast calls were examined. One hour of incubation of RBL-1 cells with all organophosphate compounds tested, except for malathion and malathion monoacid, led to an increase in histamine release. β-Hexosamini dase, an enzyme released by basophilic cells and a biochemical marker of degranulation, was not released from RBL-1 cells after 1 h of exposure to organophosphate compounds. Within 4 h, all compounds tested increased the release of histamine and β-hexosamini dase. Longer exposures led to a decrease in the concentration of the compound that was required to cause mediator release. Exposure of RPMC to organophosphate compounds, with the exception of malathion monoacid and malathion (30 min) or malathion mono acid (1 h), led to the release of histamine, but not β-hexosaminidase. Incubation of HPBB with malaoxon (51.4 ± 2.8% total histamine released), malathion diacid (25.7 ± 2.9%), β-malathion monoacid (31.4 ± 2.8%), and isomalathion (57.1 ± 17.1%) for 1 h led to the release of histamine. Only malaoxon and isomalathion caused ^-hexosaminidase release from HPBB after a 1-h incubation. Incubation of cutaneous mast cells with mala oxon and fi-monoacid for 4 h led to increased release of histamine and β-hexosaminidase at levels comparable to compound 48/80. These data suggest that malathion metabolites can cause rapid release of histamine from basophilic cells from a variety of origins and species. With prolonged incubation, malathion itself caused the release of mast-cell media tors, suggesting that the cells may be capable of metabolizing malathion. These data also indicate a disparity between the release kinetics of two different mast-cell mediators con tained in granules by organophosphates, and that there are different mechanisms of medi ator release.

EFFECTS OF MALATHION METABOLITES ON DEGRANULATION OF AND MEDIATOR RELEASE BY HUMAN AND RAT BASOPHILIC CELLS

Abstract In the present study, the effects of malathion and malathion derivatives on histamine and β-hexosaminidase release by RBL-1 cells, rat peritoneal mast cells (RPMC), and human peripheral blood basophils (HPBB) and cutaneous mast calls were examined. One hour of incubation of RBL-1 cells with all organophosphate compounds tested, except for malathion and malathion monoacid, led to an increase in histamine release. β-Hexosamini dase, an enzyme released by basophilic cells and a biochemical marker of degranulation, was not released from RBL-1 cells after 1 h of exposure to organophosphate compounds. Within 4 h, all compounds tested increased the release of histamine and β-hexosamini dase. Longer exposures led to a decrease in the concentration of the compound that was required to cause mediator release. Exposure of RPMC to organophosphate compounds, with the exception of malathion monoacid and malathion (30 min) or malathion mono acid (1 h), led to the release of histamine, but not β-hexosaminidase. Incubation of HPBB with malaoxon (51.4 ± 2.8% total histamine released), malathion diacid (25.7 ± 2.9%), β-malathion monoacid (31.4 ± 2.8%), and isomalathion (57.1 ± 17.1%) for 1 h led to the release of histamine. Only malaoxon and isomalathion caused ^-hexosaminidase release from HPBB after a 1-h incubation. Incubation of cutaneous mast cells with mala oxon and fi-monoacid for 4 h led to increased release of histamine and β-hexosaminidase at levels comparable to compound 48/80. These data suggest that malathion metabolites can cause rapid release of histamine from basophilic cells from a variety of origins and species. With prolonged incubation, malathion itself caused the release of mast-cell media tors, suggesting that the cells may be capable of metabolizing malathion. These data also indicate a disparity between the release kinetics of two different mast-cell mediators con tained in granules by organophosphates, and that there are different mechanisms of medi ator release.

A Report of the Ruggless Study for Developing Teaching Competence by Pre-Service Materials Laboratories

Research into the attitudes and skills attendant to the most ef fective use of teaching materials, developed as apart of a whole framework of research into teaching competence, was begun at Stanford University four years ago in cooperation with the Cali fornia Council on Teacher Education. A preliminary statement in the fall of 1947 entitled Factors in Teaching set the pattern for the studies that followed. With minor modifica tions in style and content, and considerable elaboration in some of its more skeletal sections, the most recent statement of Fac tors in Teaching Competence still retains the original structure, however. That is to say, it was agreed that the competent teach er was one who showed particular skills or qualities in each of the following roles: (1) as a director of learning; (2) as a medi ator of the culture; (3) as a counselor and guidance worker;(4) as an effective member of the school community; (5) as an effec tive liaison between the school and the community; and (6) as a member of the profession. That these roles overlap considerably is evident at first glance and so the document cannot possibly avoid some duplica tion in the statement of ' 'what a competent teacher can do and does. The division into these six roles has provided a rich basis for critical research, however, and has enabled profes sional teacher-educator s to evaluate programs of preparation with rather definite outcomes in mind. At Stanford, for example, a series of graduate researches have been conducted in various