Methylated DNA Immunoprecipitation-Seq with Low Input DNA Content

DNA modifications, such as methylation and hydroxymethylation, arethought to modulate gene expression, genomic imprinting, X-chromosome inactivation and silencing repetitive sequences during embryonic development.  Aberrant DNA modification lead to embryonic and postnatal abnormalities.  Comprehensive genome-wide DNA methylation and hydroxymethylation studies provide a way to thoroughly understand normal development and to identify potential epigenetic mutations in human diseases. Here we established a working protocol for methylated DNA immunoprecipitation combined with next-generation sequencing (MeDIP-seq) for low starting amounts of genomic DNA.  By using spike-in control DNA sets with standard cytosine, 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC), we demonstrate the preferential binding of antibodies to 5mC and 5hmC, respectively. MeDIP-PCRs successfully targeted highly methylated genomic loci with starting genomic DNA as low as 1 ng. The enrichment efficiency declined for constant spiked-in controls but increased for endogenous methylated region. A MeDIP-seq library was constructed starting with 1 ng DNA with the majority of fragments between 250 bp and 600 bp. The MeDIP-seq reads showed higher quality than the input control. However, after preprocessed by Cutadapt, MeDIP (97.5%) and Input (94.9%) reads showed comparable alignment rates. SeqMonk visualization tools indicated MeDIP-Seq reads were less uniformly distributed across the genome than Input reads. Several commonly known unmethylated and methylated genomic loci showed consistent methylation patterns in the MeDIP-seq data. Thus we provide proof-of-principle that MeDIP-seq technology is feasible to profile genome-wide DNA methylation in minute DNA samples, such as oocytes, early embryos and human biopsies.