Cytosine bases of the nuclear genome in higher plants are often extensively methylated.Cytosine methylation has been implicated in the silencing of both transposable elements （TEs） and endogenous genes,and loss of m...Cytosine bases of the nuclear genome in higher plants are often extensively methylated.Cytosine methylation has been implicated in the silencing of both transposable elements （TEs） and endogenous genes,and loss of methylation may have severe functional consequences.The recent methylation profiling of the entire Arabidopsis genome has provided novel insights into the extent and pattern of cytosine methylation and its relationships with gene activity.In addition,the fresh studies also revealed the more dynamic nature of this epigenetic modification across plant development than previously believed.Cytosine methylation of gene promoter regions usually inhibits transcription,but methylation in coding regions （gene-body methylation） does not generally affect gene expression.Active demethylation （though probably act synergistically with passive loss of methylation） of promoters by the 5-methyl cytosine DNA glycosylase or DEMETER （DME） is required for the uni-parental expression of imprinting genes in endosperm,which is essential for seed viability.The opinion that cytosine methylation is indispensible for normal plant development has been reinforced by using single or combinations of diverse loss-of-function mutants for DNA methyltransferases,DNA glycosylases,components involved in siRNA biogenesis and chromatin remodeling factors.Patterns of cytosine methylation in plants are usually faithfully maintained across organismal generations by the concerted action of epigenetic inheritance and progressive correction of strayed patterns.However,some variant methylation patterns may escape from being corrected and hence produce novel epialleles in the affected somatic cells.This,coupled with the unique property of plants to produce germline cells late during development,may enable the newly acquired epialleles to be inherited to future generations,which if visible to selection may contribute to adaptation and evolution.展开更多
Hepatocellular carcinoma （HCC） is one of the most common human cancers, and its incidence is still increasing in many countries. The prognosis of HCC patients remains poor, and identification of useful molecular pro...Hepatocellular carcinoma （HCC） is one of the most common human cancers, and its incidence is still increasing in many countries. The prognosis of HCC patients remains poor, and identification of useful molecular prognostic markers is required. Many recent studies have shown that functional alterations of cellcycle regulators can be observed in HCC. Among the various types of cell-cycle regulators, p16 and p27 are frequently inactivated in HCC and are considered to be potent tumor suppressors, p16, a G1-specific cell-cycle inhibitor that prevents the association of cyclindependent kinase （CDK） 4 and CDK6 with cyclin DI, is frequently inactivated in HCC via CpG methylation of its promoter region, p16 may be involved in the early steps of hepatocarcinogenesis, since p16 gene methylation has been detected in subsets of pre-neoplastic liver cirrhosis patients, p27, a negative regulator of the G1-S phase transition through inhibition of the kinase activities of Cdk2/cyclin A and Cdk2/cyclin E complexes, is now considered to be an adverse prognostic factor in HCC. In some cases of HCC with increased cell proliferation, p27 is overexpressed but inactivated by sequestration into cyclin D1-CDK4-containing complexes. Since loss of p16 is closely related to functional inactivation of p27 in HCC, investigating both p16 and p27 may be useful for precise prognostic predictions in individuals with HCC.展开更多
目的观察二氢杨梅素对人乳腺癌MCF-7细胞中第10号染色体缺失的磷酸酶和张力蛋白同源基因(phosphatase and tensin homology deleted on chromosome ten,PTEN)甲基化及其表达的影响,并探讨相关作用机制。方法以CCK-8法检测细胞活力,qRT-...目的观察二氢杨梅素对人乳腺癌MCF-7细胞中第10号染色体缺失的磷酸酶和张力蛋白同源基因(phosphatase and tensin homology deleted on chromosome ten,PTEN)甲基化及其表达的影响,并探讨相关作用机制。方法以CCK-8法检测细胞活力,qRT-PCR检测PTEN和DNA甲基转移酶(DNA methyltransferase,DNMT)DNMT1、DNMT3a、DNMT3b的mRNA表达,Western blot法检测PTEN的蛋白表达,荧光法检测细胞DNA甲基转移酶总活性,甲基化特异性PCR法(methylation-specific PCR,MSP)检测PTEN基因甲基化水平。结果细胞活力检测结果表明,二氢杨梅素可剂量依赖性降低乳腺癌MCF-7细胞活力(P<0.05);qRT-PCR和Western blot检测结果表明,二氢杨梅素可显著上调PTEN的表达(P<0.05),并呈现剂量-效应关系;MSP检测结果显示,二氢杨梅素可显著诱导MCF-7细胞PTEN基因去甲基化;qRT-PCR和荧光法检测结果显示,二氢杨梅素可显著降低MCF-7细胞DNMT1表达和DNMT活性(P<0.05)。结论二氢杨梅素显著诱导乳腺癌细胞PTEN基因去甲基化,促进其表达,其机制可能主要涉及对DNMT1表达和活性的抑制。展开更多
High rate of abortion and developmental abnormalities is thought to be closely associated with inefficient epigenetic reprogramming of the transplanted nuclei during bovine cloning. It is known that one of the importa...High rate of abortion and developmental abnormalities is thought to be closely associated with inefficient epigenetic reprogramming of the transplanted nuclei during bovine cloning. It is known that one of the important mechanisms for epigenetic reprogramming is DNA methylation. DNA methylation is established and maintained by DNA methyltransferases （DNMTs）, therefore, it is postulated that the inefficient epigenetic reprogramming of transplanted nuclei may be due to abnormal expression of DNMTs. Since DNA methylation can strongly inhibit gene expression, aberrant DNA methylation of DNMT genes may disturb gene expression. But presently, it is not clear whether the methylation abnormality of DNMT genes is related to developmental failure of somatic cell nuclear transfer embryos. In our study, we analyzed methylation patterns of the 5＇ regions of four DNMT genes including Dnmt3a, Dnmt3b, Dnmtl and Dnmt2 in four aborted bovine clones. Using bisulfite sequencing method, we found that 3 out of 4 aborted bovine clones （AF1, AF2 and AF3） showed either hypermethylation or hypomethylation in the 5＇ regions of Dnmt3a and Dnmt3b, indicating that Dnmt3a and Dnmt3b genes are not properly reprogrammed. However, the individual AF4 exhibited similar methylation level and pattern to age-matched in vitro fertilized （IVF） fetuses. Besides, we found that the 5＇ regions of Dnmtl and Dnmt2 were nearly completely unmethylated in all normal adults, IVF fetuses, sperm and aborted clones. Together, our results suggest that the aberrant methylation of Dnmt3a and Dnmt3b 5＇ regions is probably associated with the high abortion of bovine clones.展开更多
基金supported by the National Natural Science Foundation of China (No. 30870198 and 30870178)the Programme of Introducing Talents of Discipline to Universities of China (No. B07017)
文摘Cytosine bases of the nuclear genome in higher plants are often extensively methylated.Cytosine methylation has been implicated in the silencing of both transposable elements （TEs） and endogenous genes,and loss of methylation may have severe functional consequences.The recent methylation profiling of the entire Arabidopsis genome has provided novel insights into the extent and pattern of cytosine methylation and its relationships with gene activity.In addition,the fresh studies also revealed the more dynamic nature of this epigenetic modification across plant development than previously believed.Cytosine methylation of gene promoter regions usually inhibits transcription,but methylation in coding regions （gene-body methylation） does not generally affect gene expression.Active demethylation （though probably act synergistically with passive loss of methylation） of promoters by the 5-methyl cytosine DNA glycosylase or DEMETER （DME） is required for the uni-parental expression of imprinting genes in endosperm,which is essential for seed viability.The opinion that cytosine methylation is indispensible for normal plant development has been reinforced by using single or combinations of diverse loss-of-function mutants for DNA methyltransferases,DNA glycosylases,components involved in siRNA biogenesis and chromatin remodeling factors.Patterns of cytosine methylation in plants are usually faithfully maintained across organismal generations by the concerted action of epigenetic inheritance and progressive correction of strayed patterns.However,some variant methylation patterns may escape from being corrected and hence produce novel epialleles in the affected somatic cells.This,coupled with the unique property of plants to produce germline cells late during development,may enable the newly acquired epialleles to be inherited to future generations,which if visible to selection may contribute to adaptation and evolution.
文摘Hepatocellular carcinoma （HCC） is one of the most common human cancers, and its incidence is still increasing in many countries. The prognosis of HCC patients remains poor, and identification of useful molecular prognostic markers is required. Many recent studies have shown that functional alterations of cellcycle regulators can be observed in HCC. Among the various types of cell-cycle regulators, p16 and p27 are frequently inactivated in HCC and are considered to be potent tumor suppressors, p16, a G1-specific cell-cycle inhibitor that prevents the association of cyclindependent kinase （CDK） 4 and CDK6 with cyclin DI, is frequently inactivated in HCC via CpG methylation of its promoter region, p16 may be involved in the early steps of hepatocarcinogenesis, since p16 gene methylation has been detected in subsets of pre-neoplastic liver cirrhosis patients, p27, a negative regulator of the G1-S phase transition through inhibition of the kinase activities of Cdk2/cyclin A and Cdk2/cyclin E complexes, is now considered to be an adverse prognostic factor in HCC. In some cases of HCC with increased cell proliferation, p27 is overexpressed but inactivated by sequestration into cyclin D1-CDK4-containing complexes. Since loss of p16 is closely related to functional inactivation of p27 in HCC, investigating both p16 and p27 may be useful for precise prognostic predictions in individuals with HCC.
基金the National Basic Re-search Program of China (973 Program) (No. 2006CB504004 and 2006CB944004)the National Natural Science Foundation of China (No. 30430530)the Knowledge Innovation Program of the Chinese Academy of Sciences (No. KSCX2-YW-N-017).
文摘High rate of abortion and developmental abnormalities is thought to be closely associated with inefficient epigenetic reprogramming of the transplanted nuclei during bovine cloning. It is known that one of the important mechanisms for epigenetic reprogramming is DNA methylation. DNA methylation is established and maintained by DNA methyltransferases （DNMTs）, therefore, it is postulated that the inefficient epigenetic reprogramming of transplanted nuclei may be due to abnormal expression of DNMTs. Since DNA methylation can strongly inhibit gene expression, aberrant DNA methylation of DNMT genes may disturb gene expression. But presently, it is not clear whether the methylation abnormality of DNMT genes is related to developmental failure of somatic cell nuclear transfer embryos. In our study, we analyzed methylation patterns of the 5＇ regions of four DNMT genes including Dnmt3a, Dnmt3b, Dnmtl and Dnmt2 in four aborted bovine clones. Using bisulfite sequencing method, we found that 3 out of 4 aborted bovine clones （AF1, AF2 and AF3） showed either hypermethylation or hypomethylation in the 5＇ regions of Dnmt3a and Dnmt3b, indicating that Dnmt3a and Dnmt3b genes are not properly reprogrammed. However, the individual AF4 exhibited similar methylation level and pattern to age-matched in vitro fertilized （IVF） fetuses. Besides, we found that the 5＇ regions of Dnmtl and Dnmt2 were nearly completely unmethylated in all normal adults, IVF fetuses, sperm and aborted clones. Together, our results suggest that the aberrant methylation of Dnmt3a and Dnmt3b 5＇ regions is probably associated with the high abortion of bovine clones.
