Widespread differences in cortex DNA methylation of the “language gene” CNTNAP2 between humans and chimpanzees

Abstract

CNTNAP2, one of the largest genes in the human genome, has been linked to human-specific language abilities and neurodevelopmental disorders. Our hypothesis is that epigenetic rather than genetic changes have accelerated the evolution of the human brain. To compare the cortex DNA methylation patterns of human and chimpanzee CNTNAP2 at ultra-high resolution, we combined methylated DNA immunoprecipitation (MeDIP) with NimbleGen tiling arrays for the orthologous gene and flanking sequences. Approximately 1.59 Mb of the 2.51 Mb target region could be aligned and analyzed with a customized algorithm in both species. More than one fifth (0.34 Mb) of the analyzed sequence throughout the entire gene displayed significant methylation differences between six human and five chimpanzee cortices. One of the most striking interspecies differences with 28% methylation in human and 59% in chimpanzee cortex (by bisulfite pyrosequencing) lies in a region 300 bp upstream of human SNP rs7794745 which has been associated with autism and parent-of-origin effects. Quantitative real-time RT PCR revealed that the protein-coding splice variant CNTNAP2-201 is 1.6-fold upregulated in human cortex, compared with the chimpanzee. Transcripts CNTNAP2-001, -002, and -003 did not show skewed allelic expression, which argues against CNTNAP2 imprinting, at least in adult human brain. Collectively, our results suggest widespread cortex DNA methylation changes in CNTNAP2 since the human-chimpanzee split, supporting a role for CNTNAP2 fine-regulation in human-specific language and communication traits.