Multiplex bisulfite sequencing identifies differentially methylated regions in target genes in embryonic cardiomyocytes following knockdown of DNMT1 expression. Mus musculus

Purpose: This study aims to identify the differentially methylated regions in target genes in embryonic cardiomyocytes following the knockdown of DNMT1 expression. Methods: Primary cardiomyocytes were isolated from mouse embryonic day (E) 13.5 ventricles, and cultured for 48 h at 37°C to reach 70-80% confluency. Cells were transfected with either Qiagen FlexiTube GeneSolution (with 4 siRNAs) DNMT1 siRNA (#GS13433) or AllStars negative control siRNA (#1027281) at 12 nM using lipofectamine RNAiMAX (n=3 per treatment). At 72 h after transfection, cells were released with Accutase (Innovative Cell Technologies, San Diego, CA) and dissociated with Accumax (Innovative Cell Technologies). To sort cardiomyocytes, dissociated cells were stained with anti-VCAM1 antibody conjugated with allophycocyanin (APC; BioLegend, San Diego, CA), followed by magnetic sorting using anti-APC microbeads and magnetic assisted cell sorting (MACS) columns (Miltenyi Biotec, Bergisch Gladbach, Germany). DNA was extracted with the Quick-gDNA™ MicroPrep kit (Zymo Research, Irvine, CA). Genomic DNA was treated with sodium metabisulfite for bisulfite conversion. Target gene regions for fifteen target genes (two promoter regions per gene) were PCR-amplified from the bisulfite-converted DNA with ZymoTaq™ PreMix (Hot start DNA taq polymerase, ZYMO Research, Irvine, CA). The fifteen genes include Myh6, Myh7, Myh7b, Nppa, Nppb, Tnnc1, Tnni3, Tnnt2, Camta1, Camta2, Cdkn1A, Cdkn1B, Cdkn1C, Mef2c, and Mef2d. PCR products were cleaned with the ZR-96 DNA Clean & Concentrator™-5 kit (ZYMO Research). PCR products from the same genomic DNA sample were pooled at equal concentration ratio and made into an indexed sequencing library with the Nextera XT DNA Library Preparation kit and the Nextera XT Index Kit (Illumina, San Diego, CA). The Illumina-adapted libraries were pooled at equal molar ratio, spiked with 20% PhiX control libraries (Illumina), and sequenced with one 1x150 cycles run (v3) on a MiSeq sequencer (Illumina). The fastq files generated from MiSeq were uploaded to the UF Research Computing Galaxy instance developed by the University of Florida. The data were cleaned with the following steps: removed sequencing artifacts, trimmed 5’ or 3’ ends with low scores, removed adaptor contamination, and filtered low quality reads by the FastQC program. A reference genome with the amplicon sequences was built and bisulfite converted in silico with Bismark Bisulfite Mapper. The high quality sequence reads were aligned to the reference genome using Bowtie 2. Cytosine methylation counting was performed with the Bismark methylation extractor. Differential methylation was analyzed with the Methylkit package. CpG sites with false discovery rate (FDR) less than 0.05 and absolute percent methylation difference greater than 5% were considered as significant. Results: Following knockdown of DNMT1 for 72 h, differentially methylated regions were identified in the promoter CpG sites of Myh6, Myh7, Myh7b, Tnnc1, Tnni3, Tnnt2, Nppa, Nppb, Mef2c, Mef2d, Camta2, Cdkn1A, and Cdkn1C. Overall design: The DNA methylation patterns of target promoters in embryonic cardiomyocytes with knockdown of DNMT1 expression were generated by deep sequencing (n=3 for negative siRNA and n=3 for DNMT1 siRNA), using Illumina MiSeq.