Chromatin remodeling is required for transcriptional activation and repression. MRG15 (MORF4L1), a chromatin modulator, is a highly conserved protein and is present in complexes containing histone acetyltransferases (HATs) as well as histone deacetylases (HDACs). Loss of expression of MRG15 in mice and Drosophila results in embryonic lethality and fibroblast and neural stem/progenitor cells cultured from Mrg15 null mouse embryos exhibit marked proliferative defects when compared with wild type cells. To determine the role of MRG15 in cell cycle progression we performed chromatin immunoprecipitation with an antibody to MRG15 on normal human fibroblasts as they entered the cell cycle from a quiescent state, and analyzed various cell cycle gene promoters. The results demonstrated a 3-fold increase in MRG15 occupancy at the cdc2 promoter during S phase of the cell cycle and a concomitant increase in acetylated histone H4. H4 lysine 12 was acetylated at 24 hours post serum stimulation while there was no change in acetylation of lysine 16. HDAC1 and 2 were decreased at this promoter during cell cycle progression. Over-expression of MRG15 in HeLa cells activated a cdc2 promoter-reporter construct in a dose dependent manner, whereas knockdown of MRG15 resulted in decreased promoter activity. In order to implicate HAT activity, we treated cells with the HAT inhibitor anacardic acid and determined that HAT inhibition results in loss of expression of cdc2 mRNA. Further, chromatin immunoprecipitation with Tip60 localizes the protein to the same 110 bp stretch of the cdc2 promoter pulled down by MRG15. Additionally, we determined that co-transfection of MRG15 with the known associated HAT Tip60 had a cooperative effect in activating the cdc2 promoter. These results suggest that MRG15 is acting in a HAT complex involving Tip60 to modify chromatin via acetylation of histone H4 at the cdc2 promoter to activate transcription.
MRG15; Tip60; cdc2; normal human fibroblasts
Cellular senescence is the dominant phenotype over immortality. In our studies to identify senescence related genes we cloned Morf4 that induced senescence in a subset of tumor cells. Morf4 is a member of a family of 7 genes, and the Morf related genes (Mrg) on chromosomes 15 (Mrg15) and X (MrgX) are also expressed. In contrast to MORF4, MRG15 and MRGX are positive regulators of cell division. All three proteins interact with histone acetylases (HATs) and acetyltransferase (HDACs), suggesting they function in regulation of chromatin dynamics. Mrg15 knockout mice are embryonic lethal, and MEFs derived from Mrg15 null embryos proliferate poorly, enter senescence rapidly and have impaired DNA repair compared to wild type. Mrg15 null embryonic neural stem/progenitor cells also have a decreased capacity for proliferation and differentiation. Further studies are needed to determine the function of this gene family in various biological processes including neural stem/progenitor cell aging.
cellular senescence; Mrg (Morf related genes); MRG15 (Morf related gene on chromosome 15); chromatin remodelling; neural stem/progenitor cells; proliferation; differentiation; DNA damage; aging
The mammalian MRG15 gene encodes a chromodomain protein predicted to bind to chromatin via methylated histone tails. Human MORF4 encodes a related but truncated protein that is capable of promoting cellular senescence in a subset of human tumor cell lines. Drosophila contains a single homolog of human MRG15, called DmMRG15. Null mutation of MRG15 is embryonic lethal in mice and Drosophila, making study of MRG15 requirements in adults difficult. In these studies the DmMRG15 gene was over-expressed in Drosophila, during developmental stages and in adults, using a doxycycline-regulated system (Tet-on). In addition an inverted-repeated construct was designed to inactivate DmMRG15 via the RNAi pathway, and RNAi constructs were expressed using both the Tet-on system and Geneswitch system. The DmMRG15 protein was readily expressed in adult flies in a doxycycline-dependent manner. A truncated form of DmMRG15 (called DmMT1) was designed to mimic the structure of human MORF4, and expression of this mutant protein or the inverted repeat constructs inhibited fertility in females. Conditional expression of the DmMRG15 inverted-repeat constructs during larval development or in adults caused reductions in survival. These experiments indicate that Drosophila DmMRG15 gene function is required for female fertility, larval survival and adult life span, and provide reagents that should be useful for further dissecting the role of DmMRG15 in cell proliferation and aging.
senescence; chromatin; epigenetics; stem cells; aging
MRG15 is a core component of the NuA4/Tip60 histone acetyltransferase complex that modifies chromatin structure. We here demonstrate that Mrg15 null and heterozygous mouse embryonic fibroblasts exhibit an impaired DNA damage response post gamma irradiation, when compared to wild-type cells. Defects in DNA repair and cell growth, and delayed recruitment of repair proteins to sites of damage were observed. Formation of phosphorylated H2AX and 53BP1 foci was delayed in Mrg15 mutant versus wild-type cells following irradiation. These data implicate a novel role for MRG15 in DNA damage repair in mammalian cells.
MORF4; NuA4; Sin3-HDAC; ATM; 53BP1
MRGX is one of the members of MORF4/MRG family of transcriptional regulators, which are involved in cell growth regulation and cellular senescence. We have shown that MRGX and MRG15 associate with Rb in nucleoprotein complexes and regulate B-myb promoter activity. To elucidate the functions of MRGX and to explore its potential role in modulating cell growth in vivo, we have generated MrgX-deficient mice. Characterization of the expression pattern of mouse MrgX demonstrated it was ubiquitously expressed in all tissues of adult mice and also during embryogenesis and overlapped with its homolog Mrg15. MRGX and MRG15 proteins localize predominantly to the chromatin fraction in the nucleus, although a small amount of both proteins localized to the nuclear matrix. Whereas disruption of Mrg15 results in embryonic lethality, absence of MrgX did not impair mouse development and MrgX null mice are healthy and fertile. MrgX-deficient and wild-type mouse embryonic fibroblasts (MEFs) also had similar growth rates and showed no differences in cell cycle-related gene expression in response to serum stimulation. Mrg15 expression in MrgX-deficient tissues and MEFs was not upregulated compared with wild-type tissues and MEFs. MRG15 is highly conserved with orthologs present from humans to yeast and is essential for survival of mice. In contrast, MRGX, which evolved later, is expressed only in vertebrates, suggesting that the lack of phenotype of MrgX-deficient mice is secondary to a compensatory effect by the evolutionarily conserved MRG15 protein but not vice versa.
MRG15, a mammalian protein related to the mortality factor MORF4, is required for cell proliferation and embryo survival. Our genetic analysis has revealed that the Caenorhabditis elegans ortholog MRG-1 serves similar roles. Maternal MRG-1 promotes embryo survival and is required for proliferation and immortality of the primordial germ cells (PGCs). As expected of a chromodomain protein, MRG-1 associates with chromatin. Unexpectedly, it is concentrated on the autosomes and not detectable on the X chromosomes. This association is not dependent on the autosome-enriched protein MES-4. Focusing on possible roles of MRG-1 in regulating gene expression, we determined that MRG-1 is required to maintain repression in the maternal germ line of transgenes on extrachromosomal arrays, and of several X-linked genes previously shown to depend on MES-4 for repression. MRG-1 is not required for PGCs to acquire transcriptional competence or for the turn-on of expression of several PGC-expressed genes (pgl-1, glh-1, glh-4 and nos-1). By contrast to this result in PGCs, MRG-1 is required for ectopic expression of those germline genes in somatic cells lacking the NuRD complex component MEP-1. We discuss how an autosome-enriched protein might repress genes on the X chromosome, promote PGC proliferation and survival, and influence the germ versus soma distinction.
C. elegans; MRG-1; Germ line; X chromosome silencing
Human MRG15 is a transcription factor that plays a vital role in embryonic development, cell proliferation and cellular senescence. It comprises a putative chromo domain in the N-terminal part that has been shown to participate in chromatin remodeling and transcription regulation. We report here the crystal structure of human MRG15 chromo domain at 2.2 Å resolution. The MRG15 chromo domain consists of a β-barrel and a long α-helix and assumes a structure more similar to the Drosophila MOF chromo barrel domain than the typical HP1/Pc chromo domains. The β-barrel core contains a hydrophobic pocket formed by three conserved aromatic residues Tyr26, Tyr46 and Trp49 as a potential binding site for a modified residue of histone tail. However, the binding groove for the histone tail seen in the HP1/Pc chromo domains is pre-occupied by an extra β-strand. In vitro binding assay results indicate that the MRG15 chromo domain can bind to methylated Lys36, but not methylated Lys4, Lys9 and Lys27 of histone H3. These data together suggest that the MRG15 chromo domain may function as an adaptor module which can bind to a modified histone H3 in a mode different from that of the HP1/Pc chromo domains.
Neurogenesis during development depends on the coordinated regulation of self-renewal and differentiation of neural precursor cells. Chromatin regulation is a key step in self-renewal activity and fate decision of neural precursor cells. However, the molecular mechanism(s) of this regulation is not fully understood. Here, we demonstrate for the first time that MRG15, a chromatin regulator, is important for proliferation and neural fate decision of neural precursor cells. Neuroepithelia from Mrg15 deficient embryonic brain are much thinner than those from control, and apoptotic cells increase in this region. We isolated neural precursor cells from Mrg15 deficient and wild-type embryonic whole brains and produced neurospheres to measure the self-renewal and differentiation abilities of these cells in vitro. Neurospheres culture from Mrg15 deficient embryo grew less-efficiently than those from wild-type. Measurement of proliferation, using BrdU incorporation, revealed that Mrg15 deficient neural precursor cells have reduced proliferation ability and apoptotic cells do not increase during in vitro culture. The reduced proliferation of Mrg15 deficient neural precursor cells most likely accounts for the thinner neuroepithelia in Mrg15 deficient embryonic brain. Moreover, we also demonstrate Mrg15 deficient neural precursor cells are defective in differentiation into neurons in vitro. Our results demonstrate that MRG15 has more than one function in neurogenesis and defines a novel role for this chromatin regulator that integrates proliferation and cell-fate determination in neurogenesis during development.
Neural precursor cell; development; chromatin; epigenetics; gene expression
MRG15 is a member of the mortality family of transcription factors that targets a wide variety of multi-protein complexes involved in transcription regulation, DNA repair, and alternative splicing to chromatin. The structure of the apo-MRG15 MRG domain implicated in interactions with diverse proteins has been described, but not in complex with any of its targets. Here we structurally and functionally characterize the interaction between MRG15 and Pf1, two constitutively-associated subunits of the histone deacetylase-associated Rpd3S/Sin3S corepressor complex. The MRG domain adopts a structure reminiscent of the apo-state whereas the Pf1 MRG-binding domain engages two discrete hydrophobic surfaces on the MRG domain via a bipartite motif comprising an α-helix and a segment in an extended conformation, both of which are critical for high-affinity interactions. Multiple MRG15 interactors share an FxLP motif in the extended segment but equivalent sequence/helical motifs are not readily evident, implying potential diversity in MRG-recognition mechanisms.
Chromatin regulation is crucial for many biological processes such as transcriptional regulation, DNA replication, and DNA damage repair. We have found it is also important for neural stem/progenitor cell (NSC) function and neurogenesis. Here, we demonstrate that expression of the cyclin-dependent kinase inhibitor p21 is specifically up-regulated in Mrg15 deficient NSCs. Knockdown of p21 expression by p21 shRNA results in restoration of cell proliferation. This indicates that p21 is directly involved in the growth defects observed in Mrg15 deficient NSCs. Activated p53 accumulates in Mrg15 deficient NSCs and this most likely accounts for the up-regulation of p21 expression in the cells. We observed decreased p53 and p21 levels and a concomitant increase in the percentage of BrdU positive cells in Mrg15 null cultures following expression of p53 shRNA. DNA damage foci, as indicated by immunostaining for γH2AX and 53BP1, are detectable in a sub-population of Mrg15 deficient NSC cultures under normal growing conditions and the majority of p21-positive cells are also positive for 53BP1 foci. Furthermore, Mrg15 deficient NSCs exhibit severe defects in DNA damage response following ionizing radiation. Our observations highlight the importance of chromatin regulation and DNA damage response in NSC function and maintenance.
. Neural precursor cell; cell proliferation; chromatin; epigenetics; gene expression; DNA damage response
Colorectal cancer is one of the most common causes of cancer death worldwide. Using cDNA microarray containing 23 040 genes, we earlier investigated gene-expression profiles in 11 colorectal cancers for the purpose of better understanding of colorectal carcinogenesis as well as development of novel diagnostic and therapeutic strategies. MRG-binding protein (MRGBP) or C20orf20, encoding a subunit of TRRAP/TIP60-containing histone acetyltransferase complex, was up-regulated in the majority of colorectal tumours.
Methods and results:
The elevated expression of MRGBP was observed in colorectal cancer tissues by quantitative PCR as well as immunohistochemical analyses. MRGBP marginally expressed in normal vital organs. Notably, suppressed MRGBP expression by MRGBP short hairpin RNA inhibited proliferation of colorectal cancer cells. Yeast two-hybrid screening and subsequent immunoprecipitation analysis identified bromodomain containing 8 (BRD8) as an MRGBP-interacting protein. As RNA interference against BRD8 also suppressed proliferation of colorectal cancer cells, BRD8 may be an important down-stream target of MRGBP.
These results suggest that MRGBP has an important function in proliferation of cancer cells through the regulation of BRD8 and that MRGBP should be a novel therapeutic target for colorectal cancer.
C20orf20 (MRGBP); BRD8; colorectal cancer; cell proliferation
The transcriptional output at a genomic locus in eukaryotes is determined, in part, by the pattern of histone modifications that are read and interpreted by key effector proteins. The histone deacetylase activity of the evolutionarily-conserved Rpd3S/Sin3S complex is crucial for suppressing aberrant transcription from cryptic start sites within intragenic regions of actively transcribed genes. Precise targeting of the complex relies on the chromatin binding activities of the MRG15 and Pf1 subunits. Whereas the molecular target of the MRG15 chromodomain (CD) has been suggested to be H3K36me2/3, the precise molecular target of the Pf1 plant homeodomain 1 (PHD1) has remained elusive. Here we show that Pf1 PHD1 binds preferentially to the unmodified extreme N-terminus of histone H3 (H3K4me0) but not to H3K4me2/3, which are enriched in the promoter and 5′ regions of genes. Unlike previously characterized CD and PHD domains that bind to their targets with micromolar affinity, both MRG15 CD and Pf1 PHD1 bind to their targets with >100 μM affinity, offering an explanation for why both MRG15 CD and Pf1 PHD1 domains are required to target the Rpd3S/Sin3S complex to chromatin. Our results also suggest that bivalency, rather than cooperativity, is the operative mechanism by which Pf1 and MRG15 combine to engage H3 in a biologically significant manner. Finally, the studies reveal an unanticipated role of Pf1 PHD1 in engaging the MRG15 MRG domain, albeit in a Pf1 MRG-binding domain (MBD)-dependent manner, implying a key role for the MRG15 MRG-Pf1 MBD interaction in chromatin targeting of the Rpd3S/Sin3S complex.
Transcription repression; combinatorial readout; histone code; histone interactions; NMR
Transcription requires the progression of RNA polymerase II (RNAP II) through a permissive chromatin structure. Recent studies of Saccharomyces cerevisiae have demonstrated that the yeast Sin3 protein contributes to the restoration of the repressed chromatin structure at actively transcribed loci. Yet, the mechanisms underlying the restoration of the repressive chromatin structure at transcribed loci and its significance in gene expression have not been investigated in mammals. We report here the identification of a mammalian complex containing the corepressor Sin3B, the histone deacetylase HDAC1, Mrg15, and the PHD finger-containing Pf1 and show that this complex plays important roles in regulation of transcription. We demonstrate that this complex localizes at discrete loci approximately 1 kb downstream of the transcription start site of transcribed genes, and this localization requires both Pf1's and Mrg15's interaction with chromatin. Inactivation of this mammalian complex promotes increased RNAP II progression within transcribed regions and subsequent increased transcription. Our results define a novel mammalian complex that contributes to the regulation of transcription and point to divergent uses of the Sin3 protein homologues throughout evolution in the modulation of transcription.
During meiotic cell division, proper chromosome synapsis and accurate repair of DNA double strand breaks (DSBs) are required to maintain genomic integrity, loss of which leads to apoptosis or meiotic defects. The mechanisms underlying meiotic chromosome synapsis, DSB repair and apoptosis are not fully understood. Here, we report that the chromodomain-containing protein MRG-1 is an important factor for genomic integrity in meiosis in Caenorhabditis elegans. Loss of mrg-1 function resulted in a significant increase in germ cell apoptosis that was partially inhibited by mutations affecting DNA damage checkpoint genes. Consistently, mrg-1 mutant germ lines exhibited SPO-11-generated DSBs and elevated exogenous DNA damage-induced chromosome fragmentation at diakinesis. In addition, the excessive apoptosis in mrg-1 mutants was partially suppressed by loss of the synapsis checkpoint gene pch-2, and a significant number of meiotic nuclei accumulated at the leptotene/zygotene stages with an elevated level of H3K9me2 on the chromatin, which was similarly observed in mutants deficient in the synaptonemal complex, suggesting that the proper progression of chromosome synapsis is likely impaired in the absence of mrg-1. Altogether, these findings suggest that MRG-1 is critical for genomic integrity by promoting meiotic DSB repair and synapsis progression in meiosis.
apoptosis; DSB repair; synapsis; meiosis; genomic integrity; C. elegans
Protein ubiquitination is a critical component of the DNA damage response. To study the mechanism of the DNA damage-induced ubiquitination pathway, we analyzed the impact of the loss of two E3 ubiquitin ligases, RNF8 and Chfr. Interestingly, DNA damage-induced ATM activation is suppressed in RNF8 and Chfr double-deficient (DKO) cells, and DKO mice develop thymic lymphomas that are nearly diploid but harbor clonal chromosome translocations. Moreover, DKO mice and cells are hypersensitive to ionizing radiation. We show evidence that RNF8 and Chfr synergistically regulate histone ubiquitination to control histone H4K16 acetylation through MRG15-dependent acetyltransferase complexes. Through these complexes, RNF8 and CHFR affect chromatin relaxation and modulate ATM activation and DNA damage response pathways. Collectively, our findings demonstrate that two chromatin remodeling factors, RNF8 and Chfr, function together to activate ATM and maintain genomic stability in vivo.
Dynamic regulation of chromosome structure and organization is critical for fundamental cellular processes such as gene expression and chromosome segregation. Condensins are conserved chromosome-associated proteins that regulate a variety of chromosome dynamics, including axial shortening, lateral compaction, and homolog pairing. However, how the in vivo activities of condensins are regulated and how functional interactors target condensins to chromatin are not well understood. To better understand how Drosophila melanogaster condensin is regulated, we performed a yeast two-hybrid screen and identified the chromo-barrel domain protein Mrg15 to interact with the Cap-H2 condensin subunit. Genetic interactions demonstrate that Mrg15 function is required for Cap-H2-mediated unpairing of polytene chromosomes in ovarian nurse cells and salivary gland cells. In diploid tissues, transvection assays demonstrate that Mrg15 inhibits transvection at Ubx and cooperates with Cap-H2 to antagonize transvection at yellow. In cultured cells, we show that levels of chromatin-bound Cap-H2 protein are partially dependent on Mrg15 and that Cap-H2-mediated homolog unpairing is suppressed by RNA interference depletion of Mrg15. Thus, maintenance of interphase chromosome compaction and homolog pairing status requires both Mrg15 and Cap-H2. We propose a model where the Mrg15 and Cap-H2 protein–protein interaction may serve to recruit Cap-H2 to chromatin and facilitates compaction of interphase chromatin.
condensin; homolog pairing; Mrg15; chromosome structure; transvection
Histone acetyltransferase 1 is an evolutionarily conserved type B histone acetyltransferase that is thought to be responsible for the diacetylation of newly synthesized histone H4 on lysines 5 and 12 during chromatin assembly. To understand the function of this enzyme in a complex organism, we have constructed a conditional mouse knockout model of Hat1. Murine Hat1 is essential for viability, as homozygous deletion of Hat1 results in neonatal lethality. The lungs of embryos and pups genetically deficient in Hat1 were much less mature upon histological evaluation. The neonatal lethality is due to severe defects in lung development that result in less aeration and respiratory distress. Many of the Hat1−/− neonates also display significant craniofacial defects with abnormalities in the bones of the skull and jaw. Hat1−/− mouse embryonic fibroblasts (MEFs) are defective in cell proliferation and are sensitive to DNA damaging agents. In addition, the Hat1−/− MEFs display a marked increase in genome instability. Analysis of histone dynamics at sites of replication-coupled chromatin assembly demonstrates that Hat1 is not only responsible for the acetylation of newly synthesized histone H4 but is also required to maintain the acetylation of histone H3 on lysines 9, 18, and 27 during replication-coupled chromatin assembly.
The packaging of genomic DNA during replication is a highly orchestrated process. An important aspect of chromatin assembly is the processing of newly synthesized histones prior to their incorporation into chromatin. The transient acetylation of histone H3 and H4 NH2-terminal tails is a hallmark of this processing with newly synthesized molecules of histone H4 being predominantly diacetylated. This diacetylation occurs specifically on lysine residues 5 and 12 and this precise pattern is widely conserved throughout eukaryotic evolution. The acetylation of newly synthesized histones is catalyzed by type B histone acetyltransferases. Hat1 is the founding member of this class of enzymes and has been proposed to be responsible for the diacetylation of newly synthesized histone H4. Here we describe the development of a mouse knockout model of Hat1. The absence of Hat1 results in neonatal lethality due to developmental defects in the lung. Mouse embryonic fibroblasts derived from Hat1−/− mice are sensitive to DNA damaging agents and display a high level of genome instability. Biochemical analyses provide definitive evidence that Hat1 is the sole enzyme responsible for the acetylation of newly synthesized histone H4. Surprisingly, Hat1 is also necessary for the normal processing of newly synthesized histone H3.
JmjC domain-containing proteins have been shown to possess histone demethylase activity. One of these proteins is the Drosophila histone H3 lysine 4 demethylase Little imaginal discs (Lid), which has been genetically classified as a Trithorax group protein. However, contrary to the supposed function of Lid in gene activation, the biochemical activity of this protein entails the removal of a histone mark that is correlated with active transcription. To understand the molecular mechanism behind the function of Lid, we have purified a Lid-containing protein complex from Drosophila embryo nuclear extracts. In addition to Lid, the complex contains Rpd3, CG3815/Drosophila Pf1, CG13367, and Mrg15. Rpd3 is a histone deacetylase, and along with Polycomb group proteins, which antagonize the function of Trithorax group proteins, it negatively regulates transcription. By reconstituting the Lid complex, we demonstrated that the demethylase activity of Lid is not affected by its association with other proteins. However, the deacetylase activity of Rpd3 is greatly diminished upon incorporation into the Lid complex. Thus, our finding that Lid antagonizes Rpd3 function provides an explanation for the genetic classification of Lid as a positive transcription regulator.
PAM14 has been found to associate in complexes with the MORF4/MRG family of proteins as well as Rb, the tumor suppressor protein. This suggested that it might be involved in cell growth, immortalization, and/or senescence. To elucidate the in vivo function of PAM14, we characterized the expression pattern of mouse Pam14 and generated PAM14-deficient (Pam14−/−) mice. Pam14 was widely expressed in all mouse tissues and as early as 7 days during embryonic development. Despite this ubiquitous expression in wild-type mice, Pam14−/− mice were healthy and fertile. Response to mitogenic stimulation and production of interleukin-2 were the same in stimulated splenic T cells from Pam14−/− mice as in control littermates. Cell growth rates of mouse embryonic fibroblasts (MEFs) from all three genotypes were the same, and immortalized cells were obtained from all cell cultures during continuous culture. There was also no difference in expression of growth-related genes in response to serum stimulation in the null versus control MEFs. These data demonstrate that PAM14 is not essential for normal mouse development and cell cycle control. PAM14 likely acts as an adaptor protein in nucleoprotein complexes and is probably compensated for by another functionally redundant protein(s).
The male-specific-lethal (MSL) proteins in Drosophila melanogaster serve to adjust gene expression levels in male flies containing a single X chromosome to equal those in females with a double dose of X-linked genes. Together with noncoding roX RNA, MSL proteins form the “dosage compensation complex” (DCC), which interacts selectively with the X chromosome to restrict the transcription-activating histone H4 acetyltransferase MOF (males-absent-on-the-first) to that chromosome. We showed previously that MSL3 is essential for the activation of MOF's nucleosomal histone acetyltransferase activity within an MSL1-MOF complex. By characterizing the MSL3 domain structure and its associated functions, we now found that the nucleic acid binding determinants reside in the N terminus of MSL3, well separable from the C-terminal MRG signatures that form an integrated domain required for MSL1 interaction. Interaction with MSL1 mediates the activation of MOF in vitro and the targeting of MSL3 to the X-chromosomal territory in vivo. An N-terminal truncation that lacks the chromo-related domain and all nucleic acid binding activity is able to trigger de novo assembly of the DCC and establishment of an acetylated X-chromosome territory.
Histone deacetylation constitutes an important mechanism for silencing genes. The HDAC-associated mammalian Rpd3S/Sin3S corepressor complex plays key roles in repressing aberrant gene transcription from cryptic transcription initiation sites and mitigating RNA polymerase II progression in intragenic regions of actively transcribed genes. The Sin3 corepressor functions as a molecular adaptor linking HDACs on the one hand, with the chromatin targeting subunits Pf1 and MRG15, on the other. Pf1 also functions as an adaptor by interacting with MRG15 and engaging in multivalent interactions with Sin3 targeting among other domains the two N-terminal PAH domains that serve as sites of interaction with sequence-specific DNA-binding transcription factors. Here, we structurally and functionally evaluate the interaction between the PAH2 domain of mSin3A and the SID1 motif of Pf1 and find the structural aspects to be reminiscent of the interaction between the Mad1/Mxd1 transcription factor and Sin3. Pf1 residues within a highly-conserved sequence motif immediately C-terminal to SID1 appear not to be important for the interaction with Sin3 PAH2. Unexpectedly, the MRG15 subunit competes, rather than collaborate, with Sin3 for the Pf1 segment encompassing the two conserved motifs, implying competition between two subunits for another subunit of the same chromatin-modifying complex.
Rpd3S complex; transcription regulation; transcription repression; chromatin-modifying complex assembly; PAH domain; MRG domain; protein-protein interaction; Sin3 corepressor; NMR
Massive retinal gliosis (MRG) is a rare, benign intraocular condition that results from the proliferation of well-differentiated glial cells. Immunohistochemically, these cells show positivity for glial fibrillary acid protein (GFAP), neuron specific enolase (NSE), and S-100 protein. We encountered a case of a 45-year-old female with loss of vision in the left eye. She had a history of trauma to that eye two years ago. Enucleation was carried out, because malignancy was suspected due to retinal calcification. On the basis of light microscopy and immunohistochemistry (IHC) performed on the enucleated eye, it was diagnosed as massive retinal gliosis.
Enucleation; immunohistochemistry; massive retinal gliosis
Translationally controlled Tumor Protein (TCTP) is an evolutionally highly conserved protein which has been implicated in many cellular functions that are related to cell growth, death, and even the allergic response of the host. To address the physiological roles of TCTP, we generated TCTP knockout mice by targeted gene disruption. Heterozygous mutants appeared to be developmentally normal. However, homozygous mutants (TCTP−/−) were embryonic lethal. TCTP−/− embryos were smaller in size than the control littermates at all postimplantation stages examined. Although TCTP is widely expressed in both extraembryonic and embryonic tissues, the most prominent defect of the TCTP−/− embryo at embryonic stage day 5.5 (E5.5) was in its epiblast, which had a reduced number of cells compared with wild-type controls. The knockout embryos also suffered a higher incidence of apoptosis in epiblast starting about E6.5 and subsequently died around E9.5–10.5 with a severely disorganized structure. Last, we demonstrated that TCTP−/− and control mouse embryonic fibroblasts manifested similar proliferation activities and apoptotic sensitivities to various death stimuli. Taken together, our results suggest that despite that TCTP is widely expressed in many tissues or cell types, it appears to regulate cell proliferation and survival in a tissue- or cell type–specific manner.
Magnetic Resonance-guided focused Ultrasound Surgery (MRgFUS) is gaining popularity as an alternative to medical and surgical interventions in the management of symptomatic uterine fibroids. Studies have shown that it is an effective non-invasive treatment with minimal associated risks as compared to myomectomy and hysterectomy. MRgFUS can be offered to a majority of patients suffering from symptomatic uterine fibroids. It has been suggested that the use of broader inclusion criteria as well as the mitigation techniques makes it possible to offer MRgFUS to a much larger subset of patients than previously believed. This paper will describe how MRgFUS treatment for uterine fibroids is performed at the University of Malaya Medical Centre, Kuala Lumpur, Malaysia.
MRgFUS; fibroids; technique
The purpose of this study was to investigate the relationship between median rhomboid glossitis (MRG) and Candida and bacteria species, prevalence and possible association with age, gender, smoking, denture wearing, and diabetes mellitus.
Tongue examinations were performed on 4244 consecutive patients. Of all the examined patients, 30 diagnosed with MRG were selected as the study group and another 30 patients were selected as the control group, and these 2 groups were compared in terms of age and gender. Tongue cultures from these 60 patients were subjected to bacterial and mycological examinations.
MRG frequency was detected to be 0.7%. In mycological examination, Candida species were determined in 90.0% of the MRG patients and in 46.6% of the control group. This difference was statistically significant. Multivariate logistic regression indicated that diabetes mellitus and 20–39 years of age were significantly related to MRG. However, the association between MRG, gender, smoking, and 40–69 years of age was not statistically significant.
It was determined that although there was a significant association between MRG, Candida and diabetes mellitus, the possible risk factors such as gender, smoking, and denture wearing for oral candidiasis were invalid for MRG.
Candida; Median rhomboid glossitis; Diabetus mellitus