AtMBD4: A methylated DNA binding protein negatively regulates a subset of phosphate starvation genes

DNA methylation is an important epigenetic modification that governs transcriptional regulation. The methylation mark isread by a special class of proteins called methyl-CpG-binding domain proteins. The role of DNA methylation has beenfound in X-chromosome inactivation, genomic imprinting, transposon silencing, and self-incompatibility. Recently,remodeling of global DNA methylation was demonstrated in Arabidopsis during low phosphate availability. The presentstudy reports that AtMBD4 gene of Arabidopsis negatively regulates phosphate starvation. The T-DNA insertion mutation atthe AtMBD4 locus exhibited altered root architecture as compared to wild-type plants. Using microarray hybridization andanalysis, an increased transcript accumulation of 242 genes was observed in the mutant. Many of these genes were relatedto phosphate transporters and transcription factors, involved in phosphate starvation response. Comparison of data ofatmbd4 mutant with publicly available microarray data of phosphate starvation response indicated the role of AtMBD4protein in phosphate starvation response. Further, promoter analysis of up-regulated genes suggested that cis-regulatoryelements like MBS, W-box, and B1BS are more prominent in the promoters of up-regulated genes. Upon performing amethylation-specific PCR, a decreased DNA methylation in the promoter regions of up-regulated genes was observed. Theaccumulation of anthocyanin and inorganic phosphate in the atmbd4 mutant was found to be higher than the wild-typeplant. Altered root morphology, up-regulation of phosphate starvation-induced genes in atmbd4 mutant suggests thatAtMBD4 negatively regulates the phosphate starvation response.

Prokaryotic expression, purification and identification of tetrameric-protein of methyl-CpG-binding domain / 复旦学报（医学版）

Objective To express, purify and identify tetrameric protein of methyl-CpG-binding domain in E. coli. Methods The recombinant plasmid 4 × MBD-pET30b + were transformed into E. coli DH5a for clonal expansion and sequenced, then the tetrameric-proteins were expressed in E. coli BL21 (DE_3) under the induction of IPTG. Moreover, the expression products were purified by Ni-NTA chromatography, and were determined by SDS-PAGE and Western blot. Immunostain 293T cells with the proteins were analyzed by fluorescence microscope. Results The sequence analysis showed orientation right and was identical with the expectation. SDS-PAGE and Western blot demonstrated that the molecular weight of the tetrameric- protein was 46 0110 with the N-terminal His-tag and the C-terminal HA-tag. The MBD proteins can bind to the intracellular CpG DNA specifically.Conclusions The tetrameric-proteins of methyl-CpG-binding domain are successfully expressed and purified in E. coli. This results establish a groundwork for the further researches on DNA methylation.

Effect of Antisense MBD1 Gene Eukaryotic Expression Plasmid on Expression of MBD1 Gene in Human Biliary Tract Carcinoma Cells / 华中科技大学学报（医学）（英德文版）

Hypermethylation of the promoter region is one of the major mechanism of tumor suppressor gene inactivation. In order to provide a research tool for the study on the function of MBD1gene in DNA methylation and tumorigenesis, antisense MBD1 gene eukaryotic expression plasmid was constructed and transfected into human biliary tract carcinoma cell line QBC-939 to observe its effect on the expression of MBD1 mRNA and protein by using RT-PCR and FCM respectively. Following the transfection, the mRNA level of MBD1 gene decreased from 0. 912±0. 022 to 0. 215±0.017, and the protein level of MBD1 gene also decreased from (80.19±5.05) % to (35.11±4.05)%. There were very significant differences in the expression both at the transcription and post-transcription levels of MBD1 gene between non-tranfection group and the antisense MBD1 gene eukary otic expression plasmid transfection group (P＜0.01). It was suggested that transfection with the antisense MBD1 gene eukaryotic expression plasmid can significantly reduce the expression level of MBD1 gene in QBC-939, and this study may provide a valid tool for the investigation of the function of MBD1 gene and its role in biliary tract carcinoma.

Construction and identification of eukaryotic expression vector of antisense MBD1 gene fragment / 中国普通外科杂志

Objective To construct eukaryotic expression vector of antisense MBD1 gene fragment and to provide a tool for studying MBD1 gene function. Methods PCR primers were designed according to the coding sequence of MBD1 gene. Xba I and Kpn I recognition sequences and cutting sites were added to the 5' end of the sense and antisense primer respectively. The 342 bp specific PCR fragment was obtained from the cDNA of biliary tract carcinoma cell line QBC-939 using RT-PCR, the purified PCR fragment was then inserted reversely into the multiple cloning site of eukaryotic expression vector pcDNA3. 1 ( + ). The constructed recombinant plasmid was identified by PCR confirmation, Xba I and Kpn I double enzyme digestion and DNA sequencing. Results The 322 bp specific DNA band was obtained by PCR, Xba I and Kpn I double digestion produced a 327 bp and a 5. 4 kb DNA band which represent the inserted target gene fragment and the vector respectively. The sequencing result confirmed that the sequence of inserted fragment was correct. Conclusion The eukaryotic expression vector of antisense MBD1 gene fragment was constructed successfully by using gene cloning technique. It will be a useful tool for studying MBD1 gene function in DNA methylation and tumorigenesis.