In this paper, magnesium matrix hydroxyapatite composite material was prepared by electrophoretic deposition method. The optimal process parameters of electrophoretic deposition were HA suspension concentration of 0.02 kg/L, aging time of 10 days and voltage of 60 V. Animal experiment and SBF immersion experiment were used to test the biocompatibility and bioactivity of this material respectively. The SD rats were divided into control group and implant group. The implant surrounding tissue was taken to do tissue biopsy, HE dyed and organizational analysis after a certain amount of time in the SD rat body. The biological composite material was soaked in SBF solution under homeothermic condition. After 40 days, the bioactivity of the biological composite material was evaluated by testing the growth ability of apatite on composite material. The experiment results showed that magnesium matrix hydroxyapatite biological composite material was successfully prepared by electrophoretic deposition method. Tissue hyperplasia, connective tissue and new blood vessels appeared in the implant surrounding soft tissue. No infiltration of inflammatory cells of lymphocytes and megakaryocytes around the implant was found. After soaked in SBF solution, a layer bone-like apatite was found on the surface of magnesium matrix hydroxyapatite biological composite material. The magnesium matrix hydroxyapatite biological composite material could promot calcium deposition and induce bone-like apatite formation with no cytotoxicity and good biocompatibility and bioactivity.
Activation Composite 2014 Key
The various modifications made to bulk-fill composite resins using different fillers, photoinitiators, and monomers from conventional composites are expected to reduce contraction stress and increase composite resins' polymerization.[5] There are various types of bulk-fill composite resins based on their viscosity, namely, low, medium, and high viscosities and sonic-activated bulk-fill composite resins.[6] The filler size in low-viscosity bulk-fill composite resin will reduce the spread of light between the filler and the matrix so that light penetration can be more in depth.[7] High-viscosity bulk-fill composite resin, ivocerine, is used as a photoinitiator aiming to increase the degree of polymerization.[8] Even now, an instrument has been developed to condense the material with a vibration technique on composite resin application; this method uses ultrasonic power.
The polymerization quality of the composite resin can be assessed directly or indirectly. The straightforward method for assessing a degree of conversion resonance imaging, optical microscopy, and Raman or Fourier transform infrared spectroscopy,[9] whereas indirect methods include visual inspection, surface hardness consisting of ISO 4049 scraping method, and Vickers microhardness ratio.[10] The Vickers microhardness method in this study was used to evaluate the depth of cure of bulk-fill composite resin because it is easier to apply than other methods.[11] Microhardness measurements can be carried out on research samples with the Vickers test to obtain Vickers hardness ratio (VHR) data.
Several factors can influence DoC, namely, the light source used, intensity, wavelength, irradiation time, light tip size, irradiation method, chemical formulation of the organic matrix, distribution and amount of inorganic filler, type and amount of photoinitiator, and color of composite resin.[12] The low DoC indicates the low polymerization quality that a lot of free or unreacted monomer during the polymerization process.
Indentation results on sonically activated bulk-fill composite resin at a thickness of 2 mm on the top and bottom surface (a), 4 mm on the top and bottom surface (b); low-viscosity bulk-fill composite resin at a thickness of 2 mm on top and bottom surface (c), a thickness of 4 mm on top and bottom surface (d); high-viscosity bulk-fill composite resin at a thickness of 2 mm on top and bottom surface (e), and thickness of 4 mm on top and bottom surface (f)
Filler influenced the difference in the depth of cure and the characteristics of the bulk-fill composite in terms of size, volume, and weight.[17] Comparison of microhardness of high-viscosity bulk-fill composite resin with filler volume yields a positive correlation. The sonic-activated bulk-fill composite resin had the highest microhardness value and the largest filler volume, namely, 83.5 wt%/83 vol%. In contrast, high-viscosity and low-viscosity bulk-fill composite resins had the number of fillers 80 wt%/57 vol % and 70.5 wt%/47.4 vol%.
The viscosity of the composite also correlates with the type of resin matrix. Bis-GMA, as the thickest, is also the least flexible, while UDMA and TEGD-MA are the least viscous.[18] The values of microhardness or VHN in this study [Table 1] are sorted from the highest to the lowest values. Furthermore, correlated with the type of matrix, namely, (1) sonic-activated high-viscosity bulk-fill composite resin with EBPADMA, (2) high-viscosity bulk-fill composite resin with UDMA and Bis-GMA, and (3) low-viscosity bulk-fill composite resin with TEGDMA.
Biochar (BC) supported nanoscale zerovalent iron (nZVI) composite was synthesized and used as an activator for persulfate to enhance the trichloroethylene (TCE) removal in aqueous solutions. The degradation efficiency of TCE (0.15mmolL(-1)) was 99.4% in the presence of nZVI/BC (4.5mmolL(-1), nZVI to BC mass ratio was 1:5) and persulfate (4.5mmolL(-1)) within 5min, which was significantly higher than that (56.6%) in nZVI-persulfate system under the same conditions. Owing to large specific surface area and oxygen-containing functional groups of BC, nZVI/BC enhanced the SO4(-) generation and accelerated TCE degradation. On the basis of the characterization and analysis data, possible activation mechanisms of the Fe(2+)/Fe(3+) (Fe(II)/Fe(III)) redox action and the electron-transfer mediator of the BC oxygen functional groups promoting the generation of SO4(-) in nZVI/BC-persulfate system were clarified.
Company X creates a job definition for the queryInventory composite that queries their inventory. The composite includes a synchronous BPEL process and a web service as the service binding component. You associate request-specific metadata as job definitions.
Oracle Enterprise Scheduler also enables you to schedule adapters in composites to be activated and deactivated at specified times. You can schedule to activate an adapter during periods when load on the system is minimal. The fulfillment composite designed in Fulfilling Orders includes a database adapter as a service input.
Company X uses Oracle Enterprise Scheduler to activate and deactivate the database adapter using recurring schedules. Company X selects Job Requests > Define Schedules from the Scheduling Services list. Company X configures activation and deactivation job definitions for the database adapter with the details shown in Table 8-2. The database adapter is configured to active every ten minutes, and then deactivate every ten minutes.
In order to consume the Yellow River sediment as much as possible and improve the longterm stability of the Yellow River, Yellow River sediment was utilized as the main raw material to produce a composite material. Ca(OH)2 was used as alkali-activator to activate the active SiO2 and Al2O3 compositions in Yellow River sediment. 10 wt% slag was added into the mixture to further improve the strength of the composites. The effect of activity rate of the Yellow River sediment and dosage of Ca(OH)2 on the compressive strength of the Yellow River sediment-slag composite material at different curing ages was researched. XRD, SEM/ EDS, light microscope and FTIR were used to further explore the products and the microstructure of the composite material. Results showed that the active ratio of sediment had a great influence on the compressive strength of specimen. In addition, the compressive strength of specimen increased with the increase of Ca(OH)2 dosage and curing age. When the dosage of Ca(OH)2 was more than 5 wt% as well as the curing age reached 90 days, the compressive strength of the composite material could meet the engineering requirement. In the alkali-activated process, the main product was hydrated calcium silicate (C-S-H) gel, which filled up the gaps among the sediment particles and decreased the porosity of the specimen. Moreover, the CaCO3 produced by the carbonization of the C-S-H gel and excess Ca(OH)2 also played a role on the strength.
Deformed REGULATION Protein Interactions Hox proteins are transcription factors that assign positional identities along the body axis of animalembryos. Different Hox proteins have similar DNA-binding functions in vitro and require cofactors toachieve their biological functions. Cofactors can function by enhancement of the DNA-bindingspecificity of Hox proteins, as has been shown for Extradenticle (Exd). Three results support anovel mechanism for Hox cofactor function. (1) The Hox protein Deformed (Dfd) can interact with simple DNA-binding sites inDrosophila embryos in the absence of Exd, but this binding is not sufficient for transcriptionalactivation of reporter genes. (2) Either Dfd or a Dfd-VP16 hybrid (VP16 is a transcriptional activation domain) mediate much strongeractivation in embryos on a Dfd-Exd composite site than on a simple Dfd-binding site, even though thetwo sites possess similar Dfd-binding affinities. This suggests that Exd is required to release thetranscriptional activation function of Dfd independent of Exd enhancement of Dfd-binding affinity onthe composite site. (3) Transfection assays confirm that Dfd possesses an activation domain,which is suppressed in a manner dependent on the presence of the homeodomain. The regulation ofHox transcriptional activation functions may underlie the different functional specificities of proteinsbelonging to this developmental patterning family (Li, 1999a). The neutral state of Dfd on simple binding sites indicates that additional regulatory steps and regulatorysequences are required for Dfd to activate gene expression. To test the hypothesis that Dfdbinding per se is inherently neutral in embryos, a test was performed to see whether high levels of Dfd orDfd-VP16 proteins could activate transcription through simple Dfd recognition sites. In vitro, a DNAsequence consisting of two tandem copies of the simple Deformed binding site (D site or 2D), is bound by Dfd with highaffinity but not detectably bound by Exd. The affinity of Dfd protein forthe 2D-site is not enhanced by the inclusion of Exd protein (Li, 1999a). A test was performed of the embryonic function a varient of the D site reporter construct. This varient contains two tandem copiesof a core sequence, to which Dfd and Exd bind together (2ED2 sites). In vitro, the 2ED2 site is bound weaklyby Dfd protein alone, but is not bound detectably by Exd alone. Binding of Dfdto the 2ED2 site is enhanced in the presence of Exd as shown by the formation of an abundantcomplex that contains Dfd, Exd and 2ED2. The affinity of theDfd-Exd heterodimer for the 2ED2 site is approximately the same as the affinity of the Dfd proteinalone for the 2D site. Although the 2D site and the2ED2 site have very similar in vitro affinity for Dfd in the presence of Exd, the2ED2 site is much more responsive than the 2D site to either Dfd or Dfd-VP16 proteins in embryos. This strongly suggests that Exd is required to release the transcriptional activation functionof Dfd in a way that is independent of the Exd enhancement of Dfd binding affinity on the 2ED2 site.At present, the most widely accepted models propose Exd as a cofactor that has its effect on Hoxspecificity by acting to increase the binding affinity of different Hox proteins to different compositebinding sites. The results presented here indicate that Exd has other regulatory effects on Hox proteins that may play arole in the diversification of function within the Hox family (Li, 1999a). Dfd protein contains an autonomous activation domain that is functional in transfection assays whenseparated from the C-terminal half of the protein. Ontandem repeats of simple Dfd-binding sites, the function of the Dfd transcription activation domain issuppressed both in cultured cells and in embryos. In embryos, this suppression can be partially relievedby the addition of Exd-binding sites to simple Dfd-binding sites. This is apparently due to the function ofthe Exd protein, since exd genetic function is required for the relief of the suppression of Dfd activationfunction on 2ED2 sites. In cultured cells, the suppression of Dfd activation function can be conferredby the homeodomain regions from either Dfd or Ubx. Since no evidence is found that there is a directintramolecular interaction between the Dfd homeodomain and its transcriptional activation region, a model is proposed that invokes a masking factor that suppresses the function of the activationdomain by contacting the homeodomain region. In addition, it is speculated that Exd may be required toalleviate the suppressive effect of the proposed masking factor by competing for overlappingprotein-protein interaction sites on the homeodomain (Li, 1999a). DFD and UBX bind to DNA with the recognition helix in the majorgroove 3' to the TAAT core sequence and the N-terminal arm in the adjacent minor groove.The N-terminal arm of a homeodomain iscapable of distinguishing an A.T base-pair from T.A in the minor groove. Specific orientation of theN-terminal arm within the binding site appears to vary between the homeodomains and influencesthe interaction of the recognition helix with the major groove (Draganescu, 1995). The DNA sequence preferences of homeodomains encoded by four of the eight Drosophila HOM proteins were compared. One of the four, Abdominal-B, binds preferentially to a sequence with an unusual 5'-T-T-A-T-3' core, whereas the other three prefer 5'-T-A-A-T-3'. Of these latter three, the Ultrabithorax and Antennapediahomeodomains display indistinguishable preferences outside the core while Deformed differs. Thus, with three distinct binding classes defined by four HOM proteins, differences in individual site recognition may account for some but not all of HOM protein functional specificity (Ekker, 1994).Specific amino acid residues at the amino end of theUltrabithorax homeodomain are required to specifically regulate Antennapedia transcription: inthe context of a Deformed protein, these amino-end residues are sufficient to switch fromDeformed- to Ultrabithorax-like targeting specificity. Although residues in the amino end of thehomeodomain are also important in determining a Deformed-like targeting specificity, other regionsof the Deformed homeodomain are also required for full activity (Lin, 1992).Deformed possesses an acidic region just N-terminal to the homeodomain and a C-terminal sequence called the C-tail region, containing poly-glutamine and poly-asparagine tracts. Removal of the acidic domain and the C-tail region converts a chimeric Deformed/Abdominal-B protein, possessing the Abdominal-B homeodomain, from a strong activator to a repressor of a Distal-less promoter element, but has little effect on activation of an empty spiracles element. Constructs without a third domain, the N-terminal N domain, fail to show any regulatory activity. These results suggest transcriptional activation by the N domain can be modulated by acidic and C-tail domains (Zhu, 1996).A heat-shock promoter/selector gene was constructed that encodes a Deformed/Abdominal-Bchimera in which the Abdominal-B homeodomain is substituted for that of Deformed. Expression ofthis chimeric protein throughout the embryo causes morphological transformation of anteriorsegments toward more posterior identities. A number of other homeotic selector genes, all normallyrepressed by Abdominal-B, are ectopically activated by the chimeric protein. These results supportthe hypothesis that the target specificity of similar homeodomain proteins is largely determined bythe amino acid sequence of the homeodomain (Kuziora, 1990). The relevance of functional interactions between Prospero andhomeodomain proteins is supported by the observation that Prospero, together with the homeodomainprotein Deformed, is required for proper regulation of a Deformed-dependent neural-specifictranscriptional enhancer. Deformed and mouse Hoxa-5 binding to this neuronal enhancer is increased more than 10 fold by Pros. Pros reduces Eve's DNA binding to this enhancer, but does not modulate the binding of Engrailed. This interaction is unidirectional and specific, since neither Dfd, Eve nor En has an effect on Pros binding. The modulation by Pros does not require Pros binding to DNA. Pros protein modifies the trypsin sensitivity of Dfd protein, suggesting that Pros binds Dfd and is able to induce a conformation change in Dfd. Nevertheless, Pros is able to bind the Dfd neuronal autoregulatory enhancer and enhances Dfd binding to this DNA sequence. The DNA-binding and homeodomain protein-interactingactivities of Prospero are localized to its highly conserved C-terminal region, and the tworegulatory capacities are independent (Hassan, 1997). Hox transcription factors, in combination with cofactorssuch as Exd protein and itsmammalian Pbx homologs (PBC proteins), provide diverse developmental fatesto cells on the anteroposterior body axis of animal embryos.However, the mechanisms by which the different Hoxproteins and their cofactors generate those diverse fatesremain unclear. Recent findings have provided support fora model where the DNA binding sites that directly interactwith Hox-PBC heterodimers determine which member ofthe Hox protein family occupies and thereby regulates agiven target element. In the experiments reported here, the function of chimeric Hox response elements is tested, and,surprisingly, evidence is found that runs counter to this view. A21 bp cofactor binding sequence from an embryonicDeformed Hox response element (region 6), containing no Hox orHox-PBC binding sites, was combined with single ormultimeric sites that binds heterodimers of Labial-type Hoxand PBC proteins (region 3). Normally, multimerized Labial-PBCbinding sites are sufficient to trigger a Labial-specificactivation response in either Drosophila or mouse embryos.The 21 bp sequence element plays animportant role in Deformed specificity, because it is capable ofswitching a Labial-PBC binding site/response element to aDeformed response element. Thus, cofactor binding sitesthat are separate and distinct from homeodomain bindingsites can dictate the regulatory specificity of a Hox responseelement (Li, 1999b).The instructive role of factors bound to non-Hox bindingsites in controlling Hox responses is probably a generalmechanism by which different Hox proteins acquire distinctfunctions. Exd is a well-characterized example that is used ina subset of Hox-activated response elements. However, theinfluence of Exd on Hox specificity may be superseded incomplex elements that contain sequences such as region 6.How the specificity code is generated in the average Dfd orUbx response element is likely to vary depending on the celltype, the presence or absence of Exd in the cell, the stage ofdevelopment, and the extracellular signals that are received bya given response element. The putative activating cofactorbinding site(s) (GGC..AAAGC) in the region 6 element arepresent in other naturally derived Dfd response elements, so there may be an important subset of Dfd responseelements that rely on these sites for maxillary specificity. Atpresent, none of the known complex elements that respond toother Hox proteins contain good matches to the GGC..AAAGC motifs. The region6 cofactor(s) that are required to elicit a Dfd-dependentactivation response by interacting with the GGCnn(n)AAAGCmotif are not yet known. The unknown region 6 cofactors mightselectively release covert activation functions of Dfd, orinteract with Dfd to form new activation functions. In thisview, although multiple Hox proteins (e.g., Dfd and Lab) maybind to the region 3 Dfd binding site or the Lab-Exdcomposite site, only Dfd would functionally interact with thecofactors bound nearby on region 6 to activate transcription,while other Hox proteins would not (Li, 1999b). Drosophila melanogaster Hox Transcription Factors Access the RNA Polymerase II Machinery through Direct Homeodomain Binding to a Conserved Motif of Mediator Subunit Med19Hox 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. This study investigate the physical and functional interplay between Drosophila melanogaster Hox developmental TFs and MED complex proteins. The Med19 subunit was found to directly bind 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, a role was identified for Med19 in Hox-dependent target gene activation. A conserved, animal-specific motif was found 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 (Boube, 2014).The finely regulated gene transcription permitting development of pluricellular organisms involves the action of transcription factors (TFs) that bind DNA targets and convey this information to RNA polymerase II (PolII). Hox TFs, discovered through iconic mutations of the Drosophila melanogaster Bithorax and Antennapedia Complexes, play a central role in the development of a wide spectrum of animal species. Hox proteins orchestrate the differentiation of morphologically distinct segments by regulating PolII-dependent transcription of complex batteries of downstream target genes whose composition and nature are now emerging. The conserved 60 amino acid (a.a.) homeodomain (HD), a motif used for direct binding to DNA target sequences, is central to this activity. Animal orthologs of the Drosophila proteins make use of their homeodomains to play widespread and crucial roles in differentiation programs yielding the very different forms of sea urchins, worms, flies or humans. They do so by binding simple TAAT-based sequences within regulatory DNA of developmental target genes. One crucial aspect of understanding how Hox proteins transform their versatile but low-specificity DNA binding into an exquisite functional specificity involves the identification of functional partners. Known examples include the TALE HD proteins encoded by extradenticle (exd)/Pbx and homothorax (hth)/Meis, which assist Hox proteins to form stable ternary DNA-protein complexes with much-enhanced specificity. This involves contacts with the conserved Hox Hexapeptide (HX) motif near the HD N-terminus, or alternatively, with the paralog-specific UBD-A motif detected in Ubx and Abdominal-A (Abd-A) proteins. Other TFs that can serve as positional Hox partners include the segment-polarity gene products Engrailed (En) and Sloppy paired, that collaborate with Ubx and Abd-A to repress abdominal expression of Distal-less. Finally, specific a.a. residues in the HX motif, the HD and the linker separating them play a distinctive role in DNA target specificity, allowing one Hox HD region to select paralog-specific targets (Boube, 2014).Contrasting with knowledge of collaborations involving Hox and partner TFs, virtually nothing is known of what transpires at the interface with the RNA Polymerase II (PolII) machinery itself to generate an appropriate transcriptional response. The lone evidence directly linking Hox TFs to the PolII machine comes from the observation that the Drosophila TFIID component BIP2 binds the Antp HX motif (Boube, 2014).Another key component of the PolII machinery is the Mediator (MED) complex conserved from amoebae to man that serves as an interface between DNA-bound TFs and PolII. MED possesses a conserved, modular architecture characterized by the presence of head, middle, tail and optional CDK8 modules. Some of the 30 subunits composing MED appear to play a general structural role in the complex while others interact with DNA-bound TFs bridging them to PolII. Together, these subunits and the MED modules they form associate with PolII, TFs and chromatin to regulate PolII-dependent transcription (Boube, 2014).The analysis of a Drosophila skuld/Med13 mutation isolated by dose-sensitive genetic interactions with homeotic proboscipedia (pb) and Sex combs reduced (Scr) genes led to a view that MED is a Hox co-factor. However, how MED might act with Hox TFs in developmental processes has not been explored. This work pursues the hypothesis that Hox TFs modulate PolII activity through direct binding to one or more MED subunits. Starting from molecular assays, Med19 was identified as a subunit that binds to the homeodomain of representative Hox proteins through an animal-specific motif. Loss-of-function (lof) Med19 mutations isolated in this work reveal that Med19 affects Hox developmental activity and target gene regulation. Taken together, these results provide the first molecular link between Hox TFs and the general transcription machinery, showing how Med19 can act as an embedded functional partner, or 'co-factor', that directly links DNA-bound Hox homeoproteins to the PolII machinery (Boube, 2014).Hox homeodomain proteins are well-known for their roles in the control of transcription during development. Further, much is known about the composition and action of the PolII transcription machine. However, virtually nothing is known of how the information of DNA-bound Hox factors is conveyed to PolII in gene transcription. The Drosophila Ultrabithorax-like mutant affecting the large subunit of RNA PolII provokes phenotypes reminiscent of Ubx mutants, but the molecular basis of this remains unknown. The lone direct evidence linking Hox TFs to the PolII machine is binding of the Antp HX motif to the TFIID component BIP2. This study undertook to identify physical and functional links between Drosophila Hox developmental TFs and the MED transcription complex. The results unveil a novel aspect of the evolutionary Hox gene success story, extending the large repertory of proteins able to interact with the HD to include the Drosophila MED subunit Med19. HD binding to Med19 via the conserved HIM suggests this subunit is an ancient Hox collaborator. Accordingly, loss-of-function mutants reveal that Med19 contributes to normal Hox developmental function and does so at least in part via its HIM element. Thus this analysis reveals a previously unsuspected importance for Med19 in Hox-affiliated developmental functions (Boube, 2014).A fundamental property of the modular MED complex is its great flexibility that allows it to wrap around PolII and to change form substantially in response to contact with specific TFs. Recent work in the yeast S. cerevisiae places Med19 at the interfaces of the head, middle and CDK8 kinase modules. Med19 is thus well-positioned to play a pivotal regulatory role in governing MED conformation (see Model for the role of Med19 at the interface of Hox and MED). The results raise the intriguing possibility that MED structural regulation and physical contacts with DNA-bound TFs can pass through the same subunit. In agreement with this idea, recent work identified direct binding between mouse Med19 (and Med26) and RE1 Silencing Transcription Factor (REST). This binding involves a 460 a.a. region of REST encompassing its DNA-binding Zn fingers. The present work goes further, in identifying a direct link between the conserved Hox homeodomain and Med19 HIM that is the first instance for a direct, functionally relevant contact of MED with a DNA-binding motif rather than an activation domain (Boube, 2014).Med19 contributes to developmental processes with Antp (spiracle eversion), Dfd (Mx palp), and Ubx (haltere differentiation). Other phenotypes identified indicate further, non-Hox related roles for Med19. As shown in this study, complete loss of Med19 function leads to cell lethality that can be conditionally alleviated when surrounded by weakened, Minute mutation-bearing cells. These observations, that uncouple HIM-dependent functions from the role of Med19 in cell survival/proliferation, are compatible with reports correlating over-expression of human Med19/Lung Cancer Metastasis-Related Protein 1 (LCMR1) in lung cancer cells with clinical outcome. Further, RNAi-mediated knock-down of Med19 in cultured human tumor cells can reduce proliferation, and tumorigenicity when injected into nude mice. A recent whole-genome, RNAi-based screen identified Med19 as an important element of Androgen Receptor activity in prostate cancer cells where gene expression levels also correlated with clinical outcome. It will be of clear interest to examine how, and with what partners, Med19 carries out its roles in cell proliferation/survival (Boube, 2014).The role played by mammalian Med19 and Med26 in binding the REST TF, involved in inhibiting neuronal gene expression in non-neuronal cells, provides an instance of repressive Med19 regulatory function. This study found that Med19 activity is required in the Drosophila haltere disc for transcriptional activation of CG13222/edge and bab2, but is dispensable for Ubx-mediated repression of five negatively-regulated target genes. Ubx can choose to activate or it can repress, at least in part through an identified repression domain at the C-terminus just outside its homeodomain. Conversely Med19, which binds the Ubx homeodomain, appears to have much to do with activation (Boube, 2014).Concerning the mechanisms of Ubx-mediated repression, one illuminating example comes from analyses of regulated embryonic Distal-less expression. Ubx can associate combinatorially with Exd and Hth, plus the spatially restricted co-factors Engrailed or Sloppy-paired in repressing Distal-less . Engrailed in turn is able to recruit Groucho co-repressor, suggesting that localized repression involves DNA-bound Ubx/Exd/Hth/Engrailed, plus Engrailed-bound Groucho. Groucho has been proposed to function as a co-repressor that actively associates with regulatory proteins and organizes chromatin to block transcription. The yeast Groucho homolog Tup1 interacts with DNA-binding factors to mask their activation domains, thereby preventing recruitment of co-activators (including MED) necessary for activated transcription. The number of targets remains too small to be sure Med19 is consecrated to activation. Nonetheless, it will be of interest to determine whether Groucho can play a role in blocking MED/Ubx interactions that could provide an economical means for distinguishing gene activation from repression (Boube, 2014).The conserved Hox proteins and the gene complexes that encode them are well-known and widely used to study development and evolution. As to the evolutionary conservation of the Mediator transcription complex, the presence of MED constituents in far-flung eukaryotic species from unicellular parasites to humans indicates that this complex existed well before the emergence of the modern animal Hox protein complexes. The DNA-binding domains are often the most conserved elements of TF primary sequence, and in the case of the Hox HD, recent forays into 'synthetic biology' agree that this was the functional heart of the ancestral proto-Hox proteins. Indeed, Scr, Antp and Ubx mini-Hox peptides containing HX, linker and HD motifs behave to a good approximation like the full-length forms, directing appropriate gene activation and repression resulting in genetic transformations. The current results showing direct HD binding to Med19 HIM, and thus access to the PolII machinery, allow the activity of these mini-Hox proteins to be rationalized. It is surmised that at the time when the Hox HD emerged to become a major developmental transcription player, its capacity to connect with MED through specific existing sequences was a prerequisite for functional success. One expected consequence of this presumed initial encounter with Med19 (a selective pressure on both partners and subsequent refinement of binding sequences) is in agreement with the well-known conservation of Hox homeodomains, and with the observed conservation of the newly-identified HIM element in Hox-containing eumetazoans. It is imagined that subsequent evolution over the several hundred million years separating flies and mammals will have allowed this initial contact to be consolidated through subsequent binding to other MED subunits, ensuring versatile but reliable interactions at the MED-TF interface (Boube, 2014).Hox homeodomain proteins are traditionally referred to as selector or 'master' genes that determine developmental transcription programs. The low sequence specificity of Hox HD transcription factors is enhanced by their joint action with other TFs, of which prominent examples, the TALE homeodomain proteins Extradenticle/Pbx and Homothorax/Meis are considered to be Hox co-factors. However, a Hox TF in the company of Exd and Hth could still not be expected to shoulder all the regulatory tasks necessary to make a segment with all the coordinated cell-types it is made up of, and collaboration with cell-type specific TFs appears to be requisite. A useful alternative conception visualizes Hox proteins not as 'master-selectors' that act with co-factors, but as highly versatile co-factors in their own right that can act with diverse cell-specific identity factors to generate the cell types of a functional segment. A model is envisaged where a Hox protein would be central to assembling cell-specific transcription factors into TF complexes that interface with MED (Boube, 2014).Such Hox-anchored TF complexes could make use of selective HD binding to Med19 as a beach-head for more extensive access to MED, such that loss of the Hox protein would incapacitate the complex: in the case of Ubx- cells, inactivating bab2 or de-repressing sal. Accordingly, three observations suggest that binding of Hox-centered TF complexes involves additional MED subunits surrounding Med19: (1) bab2 target gene expression is entirely lost in Ubx-deficient cells but can persist in some Med19- cells; (2) edge-GFP in Med19- cells expressing Med19ΔHIM-VC was not altogether refractory to Ubx-activated edge-GFP expression; and (3) Med19ΔHIM-VC is not entirely impaired for Ubx binding, as seen in co-immunoprecipitations. Thus Hox protein input conveyed through Med19-HIM at the head-middle-Cdk8 module hinge might provide an economical contribution toward organizing TF complexes that influence overall MED conformation and hence transcriptional output. Decoding how the information-rich MED interface including Med19 accomplishes this will be an important part of understanding transcriptional specificity in evolution, development and pathology (Boube, 2014). Deformed : Biological Overview Evolutionary Homologs Regulation Developmental Biology Effects of Mutation ReferencesHome page: The Interactive Fly 1997 Thomas B. Brody, Ph.D.The Interactive Fly resides on theSociety for Developmental Biology's Web server. 2ff7e9595c
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