High throughput method of DNA methylation haplotyping
Particular aspects provide novel, high-throughput methods to quantify DNA methylation (e.g., at a single-base resolution) in an allele-specific manner. The methods comprise use of an allele-specific sequence polymorphism (e.g., allele-specific single nucleotide polymorphism; SNP) in sufficient proximity to a CpG methylation site to provide for distinguishing the methylation levels between two alleles. In particular aspects, after bisulfite modification, the genomic DNA region is PCR-amplified, and the product subjected to allele-specific pyrosequencing, and the percentage of methylation determined based on the percentage of cytosine to thymidine conversion. In further embodiments, MethyLight™ is used after bisulfite treatment. The inventive methodology has, for example, substantial utility for affording quantitative analyses in the regulation of analyses of X-inactivation, the allele-specific expression of genes (e.g., in the immune system) and junk DNA, etc., and in classifying an individual as to whether they have loss of imprinting (LOI).
1. A high-throughput method for quantifying allele-specific genomic DNA methylation, comprising:
obtaining a sample having genomic DNA, the genomic DNA comprising at least one allelic locus comprising at least one homozygous CpG dinucleotide sequence, the allelic locus also being heterozygous for at least one allele-specific sequence polymorphism, such that one member of the at least one homozygous CpG dinucleotide sequence is an allele-specific CpG dinucleotide sequence;
contacting the genomic DNA with a reagent or reagents suitable to convert cytosine, but not 5-methylcytosine, to uracil or another base dissimilar to cytosine in terms of hybridization behavior to provide converted DNA;
amplifying the converted DNA by polymerase-mediated amplification; and
quantifying the methylation level of the at least one allele-specific CpG dinucleotide sequence using a real-time methylation assay comprising the use of at least one allele-specific reagent that distinguishes the alleles based on the at least one allele-specific sequence polymorphism, wherein the at least one allele-specific sequence polymorphism is an allele-specific sequence polymorphism distinct from but sufficiently proximate to the at least one allele-specific CpG dinucleotide sequence to provide for distinguishing the methylation levels between the two alleles, and wherein the methylation assay comprises the use of at least one set of primers and at least one probe, wherein one of the primers is specific to the allele-specific sequence polymorphism on one DNA strand or on the complementary DNA strand, and wherein the at least one allele-specific CpG dinucleotide sequence is included in the at least one probe but not the primers.
2. The method of claim 1 , wherein the at least one allele-specific sequence polymorphism is an allele-specific single nucleotide polymorphism (SNP) sufficiently proximate to the at least one allele-specific CpG dinucleotide sequence to distinguish the methylation levels between the two alleles.
3. The method of claim 1 , comprising measuring the relative methylation of each parental allele by comparing the sample with an in vitro methylated DNA sample that is also heterozygous for the at least one allele-specific sequence polymorphism.
4. The method of claim 1 , wherein the methylation assay comprises a real-time, quantitative methylation analysis comprising the use of a plurality of primer pairs and a plurality of probes.
5. The method of claim 1 , wherein, where the primer specific to the allele-specific sequence polymorphism comprises a genomic cytosine residue position, the at least one primer is specific to the sequence on the converted DNA strand that is complementary to that of the genomic cytosine residue position.
6. The method of claim 1 , wherein a plurality of allele-specific CpG dinucleotide sequences are present on the at least one probe.
7. The method of claim 1 , further comprising, based on the quantifying, classifying an individual as to whether they have loss of imprinting (LOI).