DNA methylation is maintained with high fidelity in the honey bee germline and exhibits global non-functional fluctuations during somatic development

DNA methylation of active genes, also known as gene body methylation, is found in many animal and plant genomes. Despite this, the transcriptional and developmental role of such methylation remains poorly understood. Here, we explore the dynamic range of gene body methylation and its association with transcription and splicing in honey bee, an organism that targets methylation specifically to gene bodies. Our data show that gene body methylation globally fluctuates during honey bee development, with relatively high CG methylation in the embryo and adult stages and lower methylation in the larvae. We did not find a significant correlation between developmentally associated genic methylation dynamics and gene expression profiles. Furthermore, most developmentally regulated gene expression alterations occur in unmethylated genes. Tissue-specific methylation patterns, either at the level of complete genes or exons, are rare, implying robust maintenance of gene body methylation throughout the honeybee life cycle. Additionally, we show that CG methylation maintenance fluctuates in somatic cells, while reaching maximum fidelity in sperm cells. Finally, we report a Dnmt3-associated non-CG methylation signal in the gene bodies of adult bee heads that resembles the methylation patterns of mammalian brain tissue. Based on these results, we suggest that honey bee DNA methylation is distinctly regulated in the soma and germline. In the germline, methylation is efficiently maintained to preserve methylation patterns across generations. In contrast, methylation can fluctuate in somatic cells with limited division potential, as long as overall methylation of exons and genes remains at an adequate functional level. Additionally, we propose that heightened non-CG methylation may be a conserved characteristic of animal nervous systems. To investigate the dynamics of DNA methylation during honey bee development, we profiled the genome wide methylomes of eight developmental stages: sperm, worker embryo, worker larva, drone larva, worker pupa, worker head, drone head, and queen head. Quantification of the averaged CG methylation level of two biological replicates, either separately or combined, in the whole nuclear genome, as well as within specific genetic elements, including exons, introns, and repeats, revealed two main characteristics of DNA methylation in honey bee. BS-seq and RNA-seq samples.