Translational repression is a conserved mechanism in microRNA(miRNA)-guided gene silencing.In Arabidopsis,ARGONAUTE1(AGO1),the major miRNA effector,localizes in the cytoplasm for mRNA cleavage and at the endoplasmic r...Translational repression is a conserved mechanism in microRNA(miRNA)-guided gene silencing.In Arabidopsis,ARGONAUTE1(AGO1),the major miRNA effector,localizes in the cytoplasm for mRNA cleavage and at the endoplasmic reticulum(ER)for translational repression of target genes.However,the mechanism underlying miRNA-mediated translational repression is poorly understood.In particular,how the subcellular partitioning of AGO1 is regulated is largely unexplored.Here,we show that the plant hormone brassinosteroids(BRs)inhibit miRNA-mediated translational repression by negatively regulating the distribution of AGO1 at the ER in Arabidopsis thaliana.We show that the protein levels rather than the transcript levels of miRNA target genes were reduced in BR-deficient mutants but increased under BR treatments.The localization of AGO1 at the ER was significantly decreased under BR treatments while it was increased in the BR-deficient mutants.Moreover,ROTUNDIFOLIA3(ROT3),an enzyme involved in BR biosynthesis,co-localizes with AGO1 at the ER and interacts with AGO1 in a GW motif-dependent manner.Complementation analysis showed that the AGO1-ROT3 interaction is necessary for the function of ROT3.Our findings provide new clues to understand how miRNA-mediated gene silencing is regulated by plant endogenous hormones.展开更多
The specification of germ cells in zebrafish mostly relies on an inherited mechanism by which localized maternal determinants,called germ plasm,confer germline fate in the early embryo.Extensive studies have partially...The specification of germ cells in zebrafish mostly relies on an inherited mechanism by which localized maternal determinants,called germ plasm,confer germline fate in the early embryo.Extensive studies have partially allowed the identification of key regulators governing germ plasm formation and subsequent germ cell development.RNA-binding proteins,acting in concert with other germ plasm components,play essential roles in the organization of the germ plasm and the specification,migration,maintenance,and differentiation of primordial germ cells.The loss of their functions impairs germ cell formation and causes sterility or sexual conversion.Evidence is emerging that they instruct germline development through differential regulation of mRNA fates in somatic and germ cells.However,the challenge remains to decipher the complex interplay of maternal germ plasm components in germ plasm compartmentalization and germ cell specification.Because failure to control the developmental outcome of germ cells disrupts the formation of gametes,it is important to gain a complete picture of regulatory mechanisms operating in the germ cell lineage.This review sheds light on the contributions of RNA-binding proteins to germ cell development in zebrafish and highlights intriguing questions that remain open for future investigation.展开更多
Extensive studies in various plants show that the anthocyanin biosynthetic process is affected by environmental factors and regulated by many transcription factors through sophisticated regulatory networks. However, i...Extensive studies in various plants show that the anthocyanin biosynthetic process is affected by environmental factors and regulated by many transcription factors through sophisticated regulatory networks. However, it remains largely unclear about the roles of microRNA in this process. Here, we demonstrate that miR858a is a positive regulator of anthocyanin biosynthesis in Arabidopsis seedlings. Overexpression of miR858a enhances the accumulation of anthocyanins, whereas the reduced miR858a activity results in low levels of anthocyanins in STTM858 transgenic plants. We found that miR858a inhibits the expression of MYBL2, a key negative regulator of anthocyanin biosynthesis, by translational repression. In addition, ELONGATED HYPOCOTYL 5 （HYS） was shown to directly bind the MYBL2 promoter and represses its expression via specific histone modifications. Interestingly, we found that miR858a exhibits light- responsive expression in an HY5-dependent manner. Together, these results delineate the HY5- MIR858a-MYBL2 loop as a cellular mechanism for modulating anthocyanin biosynthesis, suggesting that integration of transcriptional and posttranscriptional regulation is critical for governing proper anthocyanin accumulation in response to light and other environmental factors.展开更多
MicroRNAs （miRNAs） recruit the RNA-induced silencing complex （RISC） to repress the translation of target mRNAs. While the 5＇ 7-methylguanosine cap of target mRNAs has been well known to be important for miRNA rep...MicroRNAs （miRNAs） recruit the RNA-induced silencing complex （RISC） to repress the translation of target mRNAs. While the 5＇ 7-methylguanosine cap of target mRNAs has been well known to be important for miRNA repression, the underlying mechanism is not clear. Here we show that TNRC6A interacts with elF4E2, a homo- Iogue of eIF4E that can bind to the cap but cannot interact with eIF4G to initiate translation, to inhibit the translation of target mRNAs. Downregulation of eIF4E2 relieved miRNA repression of reporter expression. Moreover, eIF4E2 downregulation increased the protein levels of endogenous IMP1, PTEN and PDCD4, whose expression are repressed by endogenous miRNAs. We further provide evidence showing that miRNA enhances elF4E2 association with the target mRNA. We propose that miRNAs recruit eI4E2 to compete with eIF4E to repress mRNA translation.展开更多
基金We are grateful to Professors Yijun Qi for providing the AGO1p::GFP-AGO1 seeds,Xuelu Wang for providing the 35S::BKI1-YFP seeds,Jianxiang Liu for providing the 35S::ER-mCherry plasmid,Hong Ma for providing theTOE1-Myc and mTOE1-Myc seeds,Xuemei Chen for providing the 35S::YFP-AGO1 plasmid,Shengben Li for providing the CSD2-HA and mCSD2-HA seeds,Fang Chang for providing the bri1-5 seeds,and Jinzhong Lin for providing ultracentrifuge equipment and technical guidance.This work was supported by grants of the National Natural Science Foundation of China(32025005,31830045,M-0398).
文摘Translational repression is a conserved mechanism in microRNA(miRNA)-guided gene silencing.In Arabidopsis,ARGONAUTE1(AGO1),the major miRNA effector,localizes in the cytoplasm for mRNA cleavage and at the endoplasmic reticulum(ER)for translational repression of target genes.However,the mechanism underlying miRNA-mediated translational repression is poorly understood.In particular,how the subcellular partitioning of AGO1 is regulated is largely unexplored.Here,we show that the plant hormone brassinosteroids(BRs)inhibit miRNA-mediated translational repression by negatively regulating the distribution of AGO1 at the ER in Arabidopsis thaliana.We show that the protein levels rather than the transcript levels of miRNA target genes were reduced in BR-deficient mutants but increased under BR treatments.The localization of AGO1 at the ER was significantly decreased under BR treatments while it was increased in the BR-deficient mutants.Moreover,ROTUNDIFOLIA3(ROT3),an enzyme involved in BR biosynthesis,co-localizes with AGO1 at the ER and interacts with AGO1 in a GW motif-dependent manner.Complementation analysis showed that the AGO1-ROT3 interaction is necessary for the function of ROT3.Our findings provide new clues to understand how miRNA-mediated gene silencing is regulated by plant endogenous hormones.
文摘The specification of germ cells in zebrafish mostly relies on an inherited mechanism by which localized maternal determinants,called germ plasm,confer germline fate in the early embryo.Extensive studies have partially allowed the identification of key regulators governing germ plasm formation and subsequent germ cell development.RNA-binding proteins,acting in concert with other germ plasm components,play essential roles in the organization of the germ plasm and the specification,migration,maintenance,and differentiation of primordial germ cells.The loss of their functions impairs germ cell formation and causes sterility or sexual conversion.Evidence is emerging that they instruct germline development through differential regulation of mRNA fates in somatic and germ cells.However,the challenge remains to decipher the complex interplay of maternal germ plasm components in germ plasm compartmentalization and germ cell specification.Because failure to control the developmental outcome of germ cells disrupts the formation of gametes,it is important to gain a complete picture of regulatory mechanisms operating in the germ cell lineage.This review sheds light on the contributions of RNA-binding proteins to germ cell development in zebrafish and highlights intriguing questions that remain open for future investigation.
文摘Extensive studies in various plants show that the anthocyanin biosynthetic process is affected by environmental factors and regulated by many transcription factors through sophisticated regulatory networks. However, it remains largely unclear about the roles of microRNA in this process. Here, we demonstrate that miR858a is a positive regulator of anthocyanin biosynthesis in Arabidopsis seedlings. Overexpression of miR858a enhances the accumulation of anthocyanins, whereas the reduced miR858a activity results in low levels of anthocyanins in STTM858 transgenic plants. We found that miR858a inhibits the expression of MYBL2, a key negative regulator of anthocyanin biosynthesis, by translational repression. In addition, ELONGATED HYPOCOTYL 5 （HYS） was shown to directly bind the MYBL2 promoter and represses its expression via specific histone modifications. Interestingly, we found that miR858a exhibits light- responsive expression in an HY5-dependent manner. Together, these results delineate the HY5- MIR858a-MYBL2 loop as a cellular mechanism for modulating anthocyanin biosynthesis, suggesting that integration of transcriptional and posttranscriptional regulation is critical for governing proper anthocyanin accumulation in response to light and other environmental factors.
文摘MicroRNAs （miRNAs） recruit the RNA-induced silencing complex （RISC） to repress the translation of target mRNAs. While the 5＇ 7-methylguanosine cap of target mRNAs has been well known to be important for miRNA repression, the underlying mechanism is not clear. Here we show that TNRC6A interacts with elF4E2, a homo- Iogue of eIF4E that can bind to the cap but cannot interact with eIF4G to initiate translation, to inhibit the translation of target mRNAs. Downregulation of eIF4E2 relieved miRNA repression of reporter expression. Moreover, eIF4E2 downregulation increased the protein levels of endogenous IMP1, PTEN and PDCD4, whose expression are repressed by endogenous miRNAs. We further provide evidence showing that miRNA enhances elF4E2 association with the target mRNA. We propose that miRNAs recruit eI4E2 to compete with eIF4E to repress mRNA translation.
