Nanog is a newly identified homeodomain gene that functions to sustain the pluripotency of embryonic stem cells.However,the molecular mechanism through which nanog regulates stem cell pluripotency remains unknown.Mous...Nanog is a newly identified homeodomain gene that functions to sustain the pluripotency of embryonic stem cells.However,the molecular mechanism through which nanog regulates stem cell pluripotency remains unknown.Mouse nanog encodes a polypeptide of 305 residues with a divergent homeodomain similar to those in the NK-2 family.The rest ofnanog contains no apparent homology to any known proteins characterized so far.It is hypothesized that nanog encodes a transcription factor that regulates stem cell pluripotency by switching on or off target genes.To test this hypothesis,we constructed fusion proteins between nanog and DNA binding domains of the yeast transcription factor Gal4 and tested the transactivation potentials of these constructs.Our data demonstrate that both regions N- and C- terminal to the homeodomain have transcription activities.Despite the fact that it contains no apparent transactivation motifs,the C-terminal domain is about 7 times as active as the N-terminal one.This unique arrangement of dual transactivators may confer nanog the flexibility and specificity to regulate downstream genes critical for both pluripotency and differentiation of stem cells.展开更多
Mammalian cell totipotency is a subject that has fascinated scientists for generations. A long lasting question whether some of the somatic cells retains totipotency was answered by the cloning of Dolly at the end of ...Mammalian cell totipotency is a subject that has fascinated scientists for generations. A long lasting question whether some of the somatic cells retains totipotency was answered by the cloning of Dolly at the end of the 20th century. The dawn of the 21st has brought forward great expectations in harnessing the power of totipotentcy in medicine. Through stem cell biology, it is possible to generate any parts of the human body by stem cell engineering. Considerable resources will be devoted to harness the untapped potentials of stem cells in the foreseeable future which may transform medicine as we know today. At the molecular level, totipotency has been linked to a singular transcription factor and its expression appears to define whether a cell should be totipotent. Named Oct4, it can activate or repress the expression of various genes. Curiously, very little is known about Oct4 beyond its ability to regulate gene expression. The mechanism by which Oct4 specifies totipotency remains entirely unresolved. In this review, we summarize the structure and function of Oct4 and address issues related to Oct4 function in maintaining totipotency or pluripotency of embryonic stem cells.展开更多
Based on GIS and statistical methods, with the help of searching historical literatures and calculating the landscape indices, the land use changes of Qian'an County in both spatial and temporal aspects from 1945 ...Based on GIS and statistical methods, with the help of searching historical literatures and calculating the landscape indices, the land use changes of Qian'an County in both spatial and temporal aspects from 1945 to 1996 has been analyzed in this paper. And the driving forces of land use changes and their ecological effects are discussed too. The main findings of this study are as follows: (1) Land use changed greatly in Qian'an during 1945-1996, characterized by a decrease in grassland, wetland and water bodies, and an increase in cultivated land, saline-alkali land, and the land for housing and other construction purposes. Grassland decreased by 175,828.66 ha, and cultivated land increased by 102,137.23 ha over the half century. Accordingly, the main landscape type changed from a steppe landscape to a managed agricultural ecosystem. (2) Results of correlation analysis show that the land use change in the study area was mainly driven by the socioeconomic factors. (3) The ecological effects of land use change in the area are characterized by serious salinization, degression of soil fertility and the weakening of landscape suitability.展开更多
Potassium antimonite was used to localize Ca2+ in the apical bud cells of spruce from July 1999 to May 2000. During the period of active growth (July 14), Calcium precipitates, an indication of Ca2+ localization, were...Potassium antimonite was used to localize Ca2+ in the apical bud cells of spruce from July 1999 to May 2000. During the period of active growth (July 14), Calcium precipitates, an indication of Ca2+ localization, were mainly distributed in vacuoles, intercellular spaces and cell walls. Few Ca2+ deposits localized in the cytosol and nucleus, showing a low level of the cytosolic and nuclear Ca2+ concentration in the warm summer. In August, some Ca2+ deposits appeared in the cytosol and nuclei, indicating that Ca2+ influx occurred in the cytosol and nucleus as the day length became shorter. From September to November, high levels of the cytosolic and nuclear Ca2+ remained. During the mid-winter (December and January), the distribution of Ca2+ deposits and the ultrastructures in the cells were altered dramatically. Plasmolysis occurred in many cells due to the protoplasmic dehydration. In addition plasmalemma invagination and nuclear chromatin aggregation also occurred. A large number of Ca2+ deposits appeared in the space between the plasmalemma and the cell wall. And also some Ca2+ deposits were distributed in the plastids. However, few Ca2+ deposits were observed in the cytosol and nuclei. By spring of the next year (May), when plants were de-acclimated and resumed active growth, Ca2+ subcellular localization essentially restored to that observed in July of the last year, i.e., the cells contained low cytosolic and nuclear Ca2+ concentrations; Ca2+ deposits were mainly distributed in the vacuoles, cell walls and intercellular spaces. The relationships between the seasonal changes of intracellular Ca2+ concentration and the development of dormancy/cold acclimation, as well as plasmolysis associated with dormancy and cold hardiness were discussed.展开更多
The source of long-wavelength aeromagnetic anomalies appears to originate from the earth's deep crust. Constrained by previous studies on geochemical, petrologic analysis, the eclogite and serpentinized peridoti...The source of long-wavelength aeromagnetic anomalies appears to originate from the earth's deep crust. Constrained by previous studies on geochemical, petrologic analysis, the eclogite and serpentinized peridotite samples from drill hole ZK703 at Donghai in the western Sulu ultrahigh-pressure (UHP) terrane, East China, were unambiguously exhumed from the lower crust and the upper mantle, providing significant information about the magnetic properties of rocks at a deeper part of the crust. Results show that the serpentinization process favors the neoformation of nearly stoichiometric magnetite, resulting in the enhancement of its magnetization up to 8.6 A/m, which is sufficient enough to contribute to some magnetic anomalies. In contrast, eclogite samples have only weaker magnetization (generally less than 0.05 A/m) compared to serpentinized peridotite. Nevertheless, experiments under the lower crustal conditions are necessary to further support these conclusions.展开更多
The application of mass spectrometry to investigations o{ gas-phase photochemistry and kinetics by flash photolysis was first reported in 1957. Mass spectrometry is advantageous and versatile for kinetics and mechani...The application of mass spectrometry to investigations o{ gas-phase photochemistry and kinetics by flash photolysis was first reported in 1957. Mass spectrometry is advantageous and versatile for kinetics and mechanism studies since it is capable of detecting many different chemical species during the course of the reaction and one can determine kinetic rates of reactant decay and product growth. When the mass spectrometer is used to determine kinetic decays and growths following pulsed photolysis, it may be called flash photolysis with time-resolved mass spectrometry(FPTRMS). While experiments using FPTRMS can obtain direct and valuable information on kinetics and mechanism o[ chemical reactions, they are limited in some cases. For example, experiments can be conducted only at limited temperature and pressure ranges. Moreover,the experimental investigation alone does not always provide sufficient information for the reaction mecha-nism study, especially for a complex reaction system. The theoretical investigations including Ab Initio cal-culations, RRKM calculations and numerial simulations are useful and supplemental tools to the experimen-tal studies. Ab initio and RRKM calculations can be used to predict rate coefficients of chemical reactions ina much wider ranges of temperature and pressure. Important information on the mechanism can also be obtained from the theoretical studies. However, the validation and accuracy of the results from the theoreticalinvestigations need to be verified or adjusted by experimental results. As an example, a study of kinetics and mechanism of CF3CHC10 radical reactions using FPTRMS combining with the theoretical calculations is reported.展开更多
Two phases of sinistral strike-slip ductile shear belts occur on the eastern margin of the Dabie orogenic belt. A muscovite ^40Ar/^39Ar plateau age of 128 Ma was obtained from mylonite in the later ductile shear zone....Two phases of sinistral strike-slip ductile shear belts occur on the eastern margin of the Dabie orogenic belt. A muscovite ^40Ar/^39Ar plateau age of 128 Ma was obtained from mylonite in the later ductile shear zone. Three muscovite samples separated from mylonites of 3 localities in the earlier ductile shear belts yield ^40Ar/^39Ar plateau ages of 192.5±0.7 Ma, 189.7±0.6 Ma and 188.7±0.7 Ma, respectively. They are interpreted as cooling ages of the earlier sinistral strike-slip deformation. It is suggested that left-lateral displacement of the Tan-Lu fault zone started in a late stage of the collision orogeny in the Dabie-Sulu orogenic belt between the North and South China plates. Therefore, the earlier Tan-Lu fault zone was syn-orogenic strike-slip tectonics. The fault zone was used again for sinistral displacement during tectonic activities of peri-Pacific regime in Early Cretaceous. It is proposed that the fault zone occurred as a transform fault during the orogenic process.展开更多
Global abrupt climate changes have been documented by various climate records, including ice cores, ocean sediment cores, lake sediment cores, cave deposits, loess deposits and pollen records. The climate system prefe...Global abrupt climate changes have been documented by various climate records, including ice cores, ocean sediment cores, lake sediment cores, cave deposits, loess deposits and pollen records. The climate system prefers to be in one of two stable states, i.e. interstadial or stadial conditions, but not in between. The transition between two states has an abrupt character. Abrupt climate changes are, in general, synchronous in the northern hemisphere and tropical regions. The timescale for abrupt climate changes can be as short as a decade. As the impacts may be poten-tially serious, we need to take actions such as reducing CO2 emissions to the atmosphere.展开更多
Magnetosomes of magnetotactic bacteria are of great interest in understanding biomineralization and possi- ble links between organisms and geomagnetic field. Fossil magnetosomes are ubiquitous in marine and lake sedim...Magnetosomes of magnetotactic bacteria are of great interest in understanding biomineralization and possi- ble links between organisms and geomagnetic field. Fossil magnetosomes are ubiquitous in marine and lake sediments and may significantly contribute to magnetic signals. In this review, we firstly introduce some characteristics of magneto- tactic bacteria, followed by considering recent progress in magnetosome formation, magnetic measurements, and iden- tification of bacterial magnetites in bulk sediments as well as their paleoenvironmental implications. Finally, we briefly discuss potential future breakthroughs in magnetosome studies and its applications.展开更多
A glacial stalagmite chronology from Nanjing has been established by the TIMS-U series dating and annual band counting methods. The annually layering sequence spanning the 3000-year period from 18179 to 14900 calendar...A glacial stalagmite chronology from Nanjing has been established by the TIMS-U series dating and annual band counting methods. The annually layering sequence spanning the 3000-year period from 18179 to 14900 calendar years before the present (aBP) was analyzed for evidence of East Asian summer monsoon precipitation variability during the Last Glacial Maximum (LGM). Power spectral analysis of the sequence shows a distinct interannual (2—7 years) band of enhanced variability suggestive of El Ni駉-Southern Oscillation (ENSO) teleconnections into East China during the LGM when climatic boundary conditions were different from those of today. The lower frequency bands (4—7 years) variability becomes weaker from 18179 to 14900 aBP, sup-porting the precession forcing model. The reappearance of the ENSO band in the coldest climatic boundary conditions during the Heinrich Event 1, however, suggests the stimula-tion of the enhanced East Asia winter monsoon to the El Ni駉 events.展开更多
This study investigated the feature of Chinese peoples?perception of SARS by surveying a stratified sample of 4231 people from 17 cities in China, and primarily pro-posed a risk perception centered predictive model of...This study investigated the feature of Chinese peoples?perception of SARS by surveying a stratified sample of 4231 people from 17 cities in China, and primarily pro-posed a risk perception centered predictive model of psy-chological behavior in crisis. The results indicated that, negative SARS-related information, especially informationof personal interest, will arouse peoples risk perception ofhigh level, and lead to irrational nervousness or scare; but positive SARS-related information, including recovery in-formation and that with measures taken by government, can decrease the level of risk perception. In the middle of May, people felt the highest level of risk on the SARS pathogens; the following are the physical health condition and infectiv-ity after recovering from SARS; they are factors that needspecial attention. SEM result analyses supported our hy-potheses in that SARS-related information affect people抯coping behavior and mental health through their riskperception, the four indices of risk assessment, feeling ofnerv- ousness, coping behavior and mental health areeffective presentimental indices for public psychological behavior in risky events.展开更多
基金supported in part by the Tsinghua University BaiRen Scholar Program,NSFC 30270287the 973 Project--2001CB5101 from The Ministry of Science and Technology of China.
文摘Nanog is a newly identified homeodomain gene that functions to sustain the pluripotency of embryonic stem cells.However,the molecular mechanism through which nanog regulates stem cell pluripotency remains unknown.Mouse nanog encodes a polypeptide of 305 residues with a divergent homeodomain similar to those in the NK-2 family.The rest ofnanog contains no apparent homology to any known proteins characterized so far.It is hypothesized that nanog encodes a transcription factor that regulates stem cell pluripotency by switching on or off target genes.To test this hypothesis,we constructed fusion proteins between nanog and DNA binding domains of the yeast transcription factor Gal4 and tested the transactivation potentials of these constructs.Our data demonstrate that both regions N- and C- terminal to the homeodomain have transcription activities.Despite the fact that it contains no apparent transactivation motifs,the C-terminal domain is about 7 times as active as the N-terminal one.This unique arrangement of dual transactivators may confer nanog the flexibility and specificity to regulate downstream genes critical for both pluripotency and differentiation of stem cells.
文摘Mammalian cell totipotency is a subject that has fascinated scientists for generations. A long lasting question whether some of the somatic cells retains totipotency was answered by the cloning of Dolly at the end of the 20th century. The dawn of the 21st has brought forward great expectations in harnessing the power of totipotentcy in medicine. Through stem cell biology, it is possible to generate any parts of the human body by stem cell engineering. Considerable resources will be devoted to harness the untapped potentials of stem cells in the foreseeable future which may transform medicine as we know today. At the molecular level, totipotency has been linked to a singular transcription factor and its expression appears to define whether a cell should be totipotent. Named Oct4, it can activate or repress the expression of various genes. Curiously, very little is known about Oct4 beyond its ability to regulate gene expression. The mechanism by which Oct4 specifies totipotency remains entirely unresolved. In this review, we summarize the structure and function of Oct4 and address issues related to Oct4 function in maintaining totipotency or pluripotency of embryonic stem cells.
基金National Key Project of Basic Research Development of China,No.G1999043406National Natural Science Foundation of China,No.30200040
文摘Based on GIS and statistical methods, with the help of searching historical literatures and calculating the landscape indices, the land use changes of Qian'an County in both spatial and temporal aspects from 1945 to 1996 has been analyzed in this paper. And the driving forces of land use changes and their ecological effects are discussed too. The main findings of this study are as follows: (1) Land use changed greatly in Qian'an during 1945-1996, characterized by a decrease in grassland, wetland and water bodies, and an increase in cultivated land, saline-alkali land, and the land for housing and other construction purposes. Grassland decreased by 175,828.66 ha, and cultivated land increased by 102,137.23 ha over the half century. Accordingly, the main landscape type changed from a steppe landscape to a managed agricultural ecosystem. (2) Results of correlation analysis show that the land use change in the study area was mainly driven by the socioeconomic factors. (3) The ecological effects of land use change in the area are characterized by serious salinization, degression of soil fertility and the weakening of landscape suitability.
基金Partly supported by the National Natural Science Foundation of China (Grant No.60050003)
文摘Potassium antimonite was used to localize Ca2+ in the apical bud cells of spruce from July 1999 to May 2000. During the period of active growth (July 14), Calcium precipitates, an indication of Ca2+ localization, were mainly distributed in vacuoles, intercellular spaces and cell walls. Few Ca2+ deposits localized in the cytosol and nucleus, showing a low level of the cytosolic and nuclear Ca2+ concentration in the warm summer. In August, some Ca2+ deposits appeared in the cytosol and nuclei, indicating that Ca2+ influx occurred in the cytosol and nucleus as the day length became shorter. From September to November, high levels of the cytosolic and nuclear Ca2+ remained. During the mid-winter (December and January), the distribution of Ca2+ deposits and the ultrastructures in the cells were altered dramatically. Plasmolysis occurred in many cells due to the protoplasmic dehydration. In addition plasmalemma invagination and nuclear chromatin aggregation also occurred. A large number of Ca2+ deposits appeared in the space between the plasmalemma and the cell wall. And also some Ca2+ deposits were distributed in the plastids. However, few Ca2+ deposits were observed in the cytosol and nuclei. By spring of the next year (May), when plants were de-acclimated and resumed active growth, Ca2+ subcellular localization essentially restored to that observed in July of the last year, i.e., the cells contained low cytosolic and nuclear Ca2+ concentrations; Ca2+ deposits were mainly distributed in the vacuoles, cell walls and intercellular spaces. The relationships between the seasonal changes of intracellular Ca2+ concentration and the development of dormancy/cold acclimation, as well as plasmolysis associated with dormancy and cold hardiness were discussed.
文摘The source of long-wavelength aeromagnetic anomalies appears to originate from the earth's deep crust. Constrained by previous studies on geochemical, petrologic analysis, the eclogite and serpentinized peridotite samples from drill hole ZK703 at Donghai in the western Sulu ultrahigh-pressure (UHP) terrane, East China, were unambiguously exhumed from the lower crust and the upper mantle, providing significant information about the magnetic properties of rocks at a deeper part of the crust. Results show that the serpentinization process favors the neoformation of nearly stoichiometric magnetite, resulting in the enhancement of its magnetization up to 8.6 A/m, which is sufficient enough to contribute to some magnetic anomalies. In contrast, eclogite samples have only weaker magnetization (generally less than 0.05 A/m) compared to serpentinized peridotite. Nevertheless, experiments under the lower crustal conditions are necessary to further support these conclusions.
文摘The application of mass spectrometry to investigations o{ gas-phase photochemistry and kinetics by flash photolysis was first reported in 1957. Mass spectrometry is advantageous and versatile for kinetics and mechanism studies since it is capable of detecting many different chemical species during the course of the reaction and one can determine kinetic rates of reactant decay and product growth. When the mass spectrometer is used to determine kinetic decays and growths following pulsed photolysis, it may be called flash photolysis with time-resolved mass spectrometry(FPTRMS). While experiments using FPTRMS can obtain direct and valuable information on kinetics and mechanism o[ chemical reactions, they are limited in some cases. For example, experiments can be conducted only at limited temperature and pressure ranges. Moreover,the experimental investigation alone does not always provide sufficient information for the reaction mecha-nism study, especially for a complex reaction system. The theoretical investigations including Ab Initio cal-culations, RRKM calculations and numerial simulations are useful and supplemental tools to the experimen-tal studies. Ab initio and RRKM calculations can be used to predict rate coefficients of chemical reactions ina much wider ranges of temperature and pressure. Important information on the mechanism can also be obtained from the theoretical studies. However, the validation and accuracy of the results from the theoreticalinvestigations need to be verified or adjusted by experimental results. As an example, a study of kinetics and mechanism of CF3CHC10 radical reactions using FPTRMS combining with the theoretical calculations is reported.
文摘Two phases of sinistral strike-slip ductile shear belts occur on the eastern margin of the Dabie orogenic belt. A muscovite ^40Ar/^39Ar plateau age of 128 Ma was obtained from mylonite in the later ductile shear zone. Three muscovite samples separated from mylonites of 3 localities in the earlier ductile shear belts yield ^40Ar/^39Ar plateau ages of 192.5±0.7 Ma, 189.7±0.6 Ma and 188.7±0.7 Ma, respectively. They are interpreted as cooling ages of the earlier sinistral strike-slip deformation. It is suggested that left-lateral displacement of the Tan-Lu fault zone started in a late stage of the collision orogeny in the Dabie-Sulu orogenic belt between the North and South China plates. Therefore, the earlier Tan-Lu fault zone was syn-orogenic strike-slip tectonics. The fault zone was used again for sinistral displacement during tectonic activities of peri-Pacific regime in Early Cretaceous. It is proposed that the fault zone occurred as a transform fault during the orogenic process.
文摘Global abrupt climate changes have been documented by various climate records, including ice cores, ocean sediment cores, lake sediment cores, cave deposits, loess deposits and pollen records. The climate system prefers to be in one of two stable states, i.e. interstadial or stadial conditions, but not in between. The transition between two states has an abrupt character. Abrupt climate changes are, in general, synchronous in the northern hemisphere and tropical regions. The timescale for abrupt climate changes can be as short as a decade. As the impacts may be poten-tially serious, we need to take actions such as reducing CO2 emissions to the atmosphere.
文摘Magnetosomes of magnetotactic bacteria are of great interest in understanding biomineralization and possi- ble links between organisms and geomagnetic field. Fossil magnetosomes are ubiquitous in marine and lake sediments and may significantly contribute to magnetic signals. In this review, we firstly introduce some characteristics of magneto- tactic bacteria, followed by considering recent progress in magnetosome formation, magnetic measurements, and iden- tification of bacterial magnetites in bulk sediments as well as their paleoenvironmental implications. Finally, we briefly discuss potential future breakthroughs in magnetosome studies and its applications.
基金the National Natural Science Foundation of China (Grant No. 40225007)
文摘A glacial stalagmite chronology from Nanjing has been established by the TIMS-U series dating and annual band counting methods. The annually layering sequence spanning the 3000-year period from 18179 to 14900 calendar years before the present (aBP) was analyzed for evidence of East Asian summer monsoon precipitation variability during the Last Glacial Maximum (LGM). Power spectral analysis of the sequence shows a distinct interannual (2—7 years) band of enhanced variability suggestive of El Ni駉-Southern Oscillation (ENSO) teleconnections into East China during the LGM when climatic boundary conditions were different from those of today. The lower frequency bands (4—7 years) variability becomes weaker from 18179 to 14900 aBP, sup-porting the precession forcing model. The reappearance of the ENSO band in the coldest climatic boundary conditions during the Heinrich Event 1, however, suggests the stimula-tion of the enhanced East Asia winter monsoon to the El Ni駉 events.
基金supported by the Knowledge Innovation Project of the Chinese Academy of Sciences(CAS)(CAS Program in key direction,Grant No.KSCX2-SW-221:Innovations’Grants of Institute of Psychology,No.2002l7)the National Natural Sciences of China(Emergency Grant No.70340002).
文摘This study investigated the feature of Chinese peoples?perception of SARS by surveying a stratified sample of 4231 people from 17 cities in China, and primarily pro-posed a risk perception centered predictive model of psy-chological behavior in crisis. The results indicated that, negative SARS-related information, especially informationof personal interest, will arouse peoples risk perception ofhigh level, and lead to irrational nervousness or scare; but positive SARS-related information, including recovery in-formation and that with measures taken by government, can decrease the level of risk perception. In the middle of May, people felt the highest level of risk on the SARS pathogens; the following are the physical health condition and infectiv-ity after recovering from SARS; they are factors that needspecial attention. SEM result analyses supported our hy-potheses in that SARS-related information affect people抯coping behavior and mental health through their riskperception, the four indices of risk assessment, feeling ofnerv- ousness, coping behavior and mental health areeffective presentimental indices for public psychological behavior in risky events.
