Junfeng Luo

Multiple gene methylation of nonsmall cell lung cancers evaluated with 3‐dimensional microarray

Aberrant DNA methylation of the CpG islands for cancer‐related genes is among the earliest and most frequent alterations in cancer and may be useful for diagnosing cancer or evaluating recurrent disease.

Microarray-based Ms-SNuPE: Near-quantitative analysis for a high-throughput DNA methylation

Aberrant DNA methylation of CpG site in the gene promoter region has been confirmed to be closely associated with carcinogenesis. In the present study, a microarray-based methylation-sensitive single-nucleotide primer extension (Ms-SNuPE) for parallel detecting changes of DNA methylation in cancer was developed. After modification by sodium sulfite, the unmethylated cytosine in the genomic DNA is converted to uracil while leaving the 5-methylcytosine unchanged, which can be detected by bifunctional primer carrying a unique sequence tag in addition to a locus-specific sequence. Because each locus has a distinct tag, the detecting reactions can be performed in a highly multiplexed fashion and the resulting product then be hybridized to the reverse complements of the sequence tags arrayed on a glass slide for methylation analysis. The calibration curves with the correlation coefficient >0.97 were established, which suggested that the method could be used in near-quantitative DNA methylation analysis. Two breast tumor-related genes (E-cad and p16) are successfully analyzed by two group primers (22 primers total), and the results are compatible with that of methylation-specific PCR (MSP). Our research proved that the method is simple and inexpensive, and could be applied as a high-throughput tool to quantitatively determine methylation status of the investigated genes.

Genotyping of multiple single nucleotide polymorphisms with hyperbranched rolling circle amplification and microarray

BACKGROUND The emerging role of single nucleotide polymorphisms (SNPs) in clinical diagnostics and studies has created a need for simple and high-throughput genotyping methods. Previously, we developed a 3-dimensional polyacrylamide gel-based microarray (3-D microarray) of PCR-product. This method can detect single SNP locus from multiple DNA samples on one chip. METHODS Hyperbranched rolling circle amplification (HRCA) was used to recognize different SNP loci and amplify the fragments from genomic samples. Different HRCA products were used to fabricate the 3-D microarray, and dual-color fluorescent probes were used to detect signals. RESULTS This assay was applied to genotype 2 SNP loci from a set of 6 genomic DNA samples on one chip. Universal acryl-modified primer and one pair of dual-color fluorescent probes were used for all sample detection to reduce the cost. We demonstrate that this assay can detect 10 ng genomic DNA. CONCLUSIONS Combination of HRCA and 3-D microarray allows parallel discrimination of different alleles from different samples on a single chip. It is a feasible method for high-throughput mutation analysis and disease diagnosis.

A novel method to quantify local CpG methylation density by regional methylation elongation assay on microarray

BackgroundDNA methylation based techniques are important tools in both clinical diagnostics and therapeutics. But most of these methods only analyze a few CpG sites in a target region. Indeed, difference of site-specific methylation may also lead to a change of methylation density in many cases, and it has been found that the density of methylation is more important than methylation of single CpG site for gene silencing.ResultsWe have developed a novel approach for quantitative analysis of CpG methylation density on the basis of microarray-based hybridization and incorporation of Cy5-dCTP into the Cy3 labeled target DNA by using Taq DNA Polymerase on microarray. The quantification is achieved by measuring Cy5/Cy3 signal ratio which is proportional to methylation density. This methylation-sensitive technique, termed RMEAM (regional methylation elongation assay on microarray), provides several advantages over existing methods used for methylation analysis. It can determine an exact methylation density of the given region, and has potential of high throughput. We demonstrate a use of this method in determining the methylation density of the promoter region of the tumor-related gene MLH1, TERT and MGMT in colorectal carcinoma patients.ConclusionThis technique allows for quantitative analysis of regional methylation density, which is the representative of all allelic methylation patterns in the sample. The results show that this technique has the characteristics of simplicity, rapidness, specificity and high-throughput.

Detection method for methylation density on microarray using methyl-CpG-binding domain protein.

A method for determining methylation density of target CpG islands has been established. In the method, DNA microarray was prepared by spotting a set of PCR products amplified from bisulfite-converted sample DNAs. The PCR products on the microarray were treated by SssI methyltransferase and labeled with TAMRA fluorescence. A recombinant, antibody-like methyl-CpG-binding protein labeled with Cy5 fluorescence was used to identify symmetrical methyl-CpG dinucleotide of the PCR products on the microarray. By use of a standard curve with control mixtures, the ratio of two fluorescence signals can be converted into percentage values to assess methylation density of targeted fragments. We obtained the methylation density of six CpG islands on the two tumor suppressor genes of CDK2A and CDK2B from seven cancer cell line samples and two normal blood samples. The validity of this method was tested by bisulfite sequencing. This method not only allows the quantitative analysis of regional methylation density of a set of given genes but also could provide information of methylation density for a large amount of clinical samples.