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Yehudit Bergman - One of the best experts on this subject based on the ideXlab platform.

  • g9a mediated irreversible epigenetic inactivation of oct 3 4 during early embryogenesis
    Nature Cell Biology, 2006
    Co-Authors: Nirit Feldman, Ariela Gerson, Jia Fang, Yi Zhang, Yoichi Shinkai, Howard Cedar, Yehudit Bergman
    Abstract:

    Oct-3/4 is a POU domain homeobox gene that is expressed during gametogenesis and in early embryonic cells1,2, where it has been shown to be important for maintaining pluripotency3. Following implantation, this gene undergoes a novel multi-step programme of inactivation. Transcriptional repression is followed by a pronounced increase in histone H3 methylation on Lys 9 that is mediated by the SET-containing protein, G9a. This step sets the stage for local heterochromatinization via the binding of HP1 and is required for subsequent de novo methylation at the promoter by the enzymes Dnmt3a/3b. Genetic studies show that these epigenetic changes actually have an important role in the inhibition of Oct-3/4 re-expression, thereby preventing reprogramming.

  • retinoic acid represses oct 3 4 gene expression through several retinoic acid responsive elements located in the promoter enhancer region
    Molecular and Cellular Biology, 1994
    Co-Authors: Eli Pikarsky, Hava Sharir, Etti Benshushan, Yehudit Bergman
    Abstract:

    The Oct-3/4 gene product, which belongs to the POU family of transcription factors, is a good candidate for regulating initial differentiation decisions. It is expressed in the earliest stages of embryogenesis and repressed in subsequent stages. Retinoic acid (RA)-induced differentiation of embryonal carcinoma (EC) cells is accompanied by decreased expression of the Oct-3/4 gene. Previous findings show that sequences in the Oct-3/4 enhancer region (designated RARE1) are targets for RA-mediated repression (H. Okazawa, K. Okamoto, F. Ishino, T. Ishino-Kaneko, S. Takeda, Y. Toyoda, M. Muramatsu, and H. Hamada, EMBO J. 10:2997-3005, 1991). Our present results demonstrate conclusively that the TATA-less Oct-3/4 promoter is also a target for RA-induced repression. We identified a novel cis element in the Oct-3/4 promoter harbors a putative Sp1 binding site and a RA-responsive element (designated RAREoct), which are juxtaposed to one another. Protein binding to the Sp1 site is independent of protein binding to the RAREoct sequence. Unlike the RARE1 situated in the Oct-3/4 enhancer which does not contain a typical RAR recognition site, the RAREoct identified in this study consists of three directly repeated motifs that exhibit extensive homology to RARE sequences located in RA-responsive genes. Moreover, the RAREoct shows different DNA-binding characteristics and DNase I footprint patterns with nuclear proteins isolated from undifferentiated versus RA-differentiated EC cells. This suggests that the RAREoct element binds different nuclear proteins in RA-treated and untreated EC cells which most probably belong to the RA receptor, retinoid X receptor, or orphan receptor families of transcription factors. Using site-directed mutagenesis, we show that the RAREoct contributes to the transcriptional activation of Oct-3/4 promoter in P19 cells and, most interestingly, mediates the RA-induced repression in RA-differentiated EC cells. Thus, the RAREoct element could be one of the points of integration of several signalling pathways influencing Oct-3/4 expression. In accordance with the suggestion that suppression of Oct-3/4 expression is a crucial step during embryogenesis, the Oct-3/4 upstream region contains multiple targets for RA-induced repression, probably to ensure accurate and prompt repression of Oct-3/4 expression. It is possible that these repressors are differentially used at specific stages of development in response to various signals.

  • extinction of oct 3 4 gene expression in embryonal carcinoma x fibroblast somatic cell hybrids is accompanied by changes in the methylation status chromatin structure and transcriptional activity of the oct 3 4 upstream region
    Molecular and Cellular Biology, 1993
    Co-Authors: Etti Benshushan, Eli Pikarsky, Avihu Klar, Yehudit Bergman
    Abstract:

    In this study we evaluate, for the first time, the molecular mechanism that underlies the extinction of a tissue-specific transcription factor, Oct-3/4, in somatic cell hybrids and compared it with its down-regulation in retinoic acid (RA)-treated embryonal carcinoma (EC) cells. The Oct-3/4 gene, which belongs to the POU family of transcription factors and is abundantly expressed in EC (OTF9-63) cells, provides an excellent model system with which to study the extinction phenomenon. Unlike other genes whose expression has been repressed in hybrid cells but not during in vivo differentiation, Oct-3/4 expression is dramatically repressed in OTF9-63 x fibroblast hybrids and also during embryogenesis. The ectopic expression of Oct-3/4 in hybrid cells under a constitutive promoter is sufficient for transcriptional activation of an octamer-dependent promoter. These results argue against the possibility that fibroblasts contain a direct repressor which binds directly to the octamer sequence and prevents Oct-3/4 protein from binding. The extinction of Oct-3/4 binding activity in the hybrid cells occurs at the level of mRNA transcription, similarly to the repression of Oct-3/4 transcription during in vivo differentiation. This shutdown of Oct-3/4 transcription in hybrid cells and in RA-treated EC cells is accompanied by de novo methylation of its 1.3-kb upstream region. In contrast to EC cells, in which this region is sensitive to MspI digestion, in hybrid cells and in RA-treated EC cells, the Oct-3/4 upstream region is resistant to MspI digestion, which suggests a change in its chromatin structure. Furthermore, extinction is not restricted to the endogenous Oct-3/4 gene but is also exerted upon a transiently transfected reporter gene driven by the Oct-3/4 upstream region. Thus, changes in the cellular activity of trans-acting factors acting on the upstream region also contribute to the inability of the hybrid and RA-treated EC cells to generate Oct-3/4 transcripts. In conclusion, this study draws a connection between the shutdown of Oct-3/4 expression in RA-differentiated EC cells and its extinction in hybrid cells. In both systems, repression of Oct-3/4 expression is achieved through changes in the methylation status, chromatin structure, and transcriptional activity of the Oct-3/4 upstream regulatory region.

C W Chu - One of the best experts on this subject based on the ideXlab platform.

  • magnetoelectric effect and spontaneous polarization in hofe 3 bo 3 4 and ho 0 5 nd 0 5 fe 3 bo 3 4
    Physical Review B, 2009
    Co-Authors: R P Chaudhury, Fei Yen, Bernd Lorenz, Y Y Sun, L N Bezmaternykh, V L Temerov, C W Chu
    Abstract:

    The thermodynamic, magnetic, dielectric, and magnetoelectric properties of ${\text{HoFe}}_{3}{({\text{BO}}_{3})}_{4}$ and ${\text{Ho}}_{0.5}{\text{Nd}}_{0.5}{\text{Fe}}_{3}{({\text{BO}}_{3})}_{4}$ are investigated. Both compounds show a second order Ne\'el transition above 30 K and a first-order spin reorientation transition below 10 K. ${\text{HoFe}}_{3}{({\text{BO}}_{3})}_{4}$ develops a spontaneous electrical polarization below the Ne\'el temperature $({T}_{N})$ which is diminished in external magnetic fields. No magnetic-field induced increase of the polarization could be observed in ${\text{HoFe}}_{3}{({\text{BO}}_{3})}_{4}$. In contrast, the solid solution ${\text{Ho}}_{0.5}{\text{Nd}}_{0.5}{\text{Fe}}_{3}{({\text{BO}}_{3})}_{4}$ exhibits both, a spontaneous polarization below ${T}_{N}$ and a positive magnetoelectric effect at higher fields that extends to high temperatures. The superposition of spontaneous polarization, induced by the internal magnetic field in the ordered state, and the magnetoelectric polarizations due to the external field results in a complex behavior of the total polarization measured as a function of temperature and field.

Haibin Song - One of the best experts on this subject based on the ideXlab platform.

  • synthesis crystal structure and biological activity of 4 methyl 1 2 3 thiadiazole containing 1 2 4 triazolo 3 4 b 1 3 4 thiadiazoles
    Journal of Agricultural and Food Chemistry, 2010
    Co-Authors: Zhikun Yang, Haike Zhang, Na Mi, Qingxiang Zheng, Huan Wang, Haibin Song
    Abstract:

    Heterocyclic compounds play an important role as the main sources of lead molecules of agrochemicals. Synthesis and biological activity of thiadiazole-containing 1,2,4-triazolo[3,4-b][1,3,4]-thiadiazoles were seldom reported. To find novel lead compounds with various biological activities, a series of 6-substituted-3-(4-methyl-1,2,3-thiadiazolyl)[1,2,4]triazolo[3,4-b][1,3,4]thiadizoles were rationally designed and synthesized according to the principle of combinations of bioactive substructures by the condensation of 3-(4-methyl-1,2,3-thiadiazolyl)-4-amino-1,2,4-triazole-5-thione with various carboxylic acids and phosphorus oxychloride. All newly synthesized compounds were identified by proton nuclear magnetic resonance (1H NMR), infrared spectroscopy (IR), electroionization mass spectrometry (EI/MS), and elementary analysis. The crystal structure of 3-(4-methyl-1,2,3-thiadiazolyl)-6-(4-methylphenyl)[1,2,4]triazolo[3,4-b][1,3,4]thiadizole was determined by X-ray diffraction crystallography. In this crysta...

Shigeru Ohno - One of the best experts on this subject based on the ideXlab platform.

  • molecular and crystal structures of 2 3 4 6 1 3 4 6 octa o acetyl β sophorose methyl 2 3 4 6 3 4 6 hepta o acetyl β sophoroside and methyl 2 3 4 6 3 4 hexa o acetyl 6 deoxy β sophoroside
    Carbohydrate Research, 1995
    Co-Authors: Masaki Ikegami, Tomoya Sato, Kouichi Suzuki, Keiichi Noguchi, Kenji Okuyama, Shinichi Kitamura, Ken'ichi Takeo, Shigeru Ohno
    Abstract:

    The molecular and crystal structures of 2,3,4,6,1′,3′,4′,6′-octa-O-acetyl-β-sophorose (β-sophorose octaacetate), methyl 2,3,4,6,3′,4′,6′-hepta-O-acetyl-β-sophoroside (methyl β-sophoroside heptaacetate), and methyl 2,3,4,6,3′,4′-hexa-O-acetyl-6′-deoxy-β-sophoroside (methyl 6′-deoxy-β-sophoroside heptaacetate) were determined by X-ray diffraction. All structures were obtained by the direct method and refined by the full-matrix least-squares procedure. The crystal data and final R values are as follows: (β-sophorose octaacetate, C28O19H38, monoclinic, P21, a = 15.529(4), b = 10.958(2), c = 10.804(2) A, β = 107.73(3)°, Dobsd = 1.285 g cm−3, Dcalcd = 1.288 g cm−3, Z = 2, R = 0.052, RW = 0.052; methyl β-sophoroside heptaacetate, C27O18H38, orthorhombic, P212121, a = 20.992(5), b = 27.642(7), c = 5.730(2) A, Dobsd = 1.305 g cm−3, Dcalcd = 1.295 g cm−3, Z = 4, R = 0.064, RW = 0.066; methyl 6′-deoxy-β-sophoroside hexaacetate, C25O16H36, hexagonal, P65, a = b = 15.136(2), c = 23.534(4) A, Dcalcd = 1.264 g cm−3, Z = 6, R = 0.079, RW = 0.064. All the d-glucose residues have the 4C1 pyranose conformation. These three molecules interact with their surrounding molecules by van der Waals forces, only. Conformational angles of φ and ω at the β (1 → 2) glycosidic linkage of these compounds are similar to each other and close to the energetically minimum positions. All the primary acetate substituents at C-6 take a gauche-gauche conformation.

Zhikun Yang - One of the best experts on this subject based on the ideXlab platform.

  • synthesis crystal structure and biological activity of 4 methyl 1 2 3 thiadiazole containing 1 2 4 triazolo 3 4 b 1 3 4 thiadiazoles
    Journal of Agricultural and Food Chemistry, 2010
    Co-Authors: Zhikun Yang, Haike Zhang, Na Mi, Qingxiang Zheng, Huan Wang, Haibin Song
    Abstract:

    Heterocyclic compounds play an important role as the main sources of lead molecules of agrochemicals. Synthesis and biological activity of thiadiazole-containing 1,2,4-triazolo[3,4-b][1,3,4]-thiadiazoles were seldom reported. To find novel lead compounds with various biological activities, a series of 6-substituted-3-(4-methyl-1,2,3-thiadiazolyl)[1,2,4]triazolo[3,4-b][1,3,4]thiadizoles were rationally designed and synthesized according to the principle of combinations of bioactive substructures by the condensation of 3-(4-methyl-1,2,3-thiadiazolyl)-4-amino-1,2,4-triazole-5-thione with various carboxylic acids and phosphorus oxychloride. All newly synthesized compounds were identified by proton nuclear magnetic resonance (1H NMR), infrared spectroscopy (IR), electroionization mass spectrometry (EI/MS), and elementary analysis. The crystal structure of 3-(4-methyl-1,2,3-thiadiazolyl)-6-(4-methylphenyl)[1,2,4]triazolo[3,4-b][1,3,4]thiadizole was determined by X-ray diffraction crystallography. In this crysta...