Parent-of-origin effects on transcription and chromatin regulation in reproductive caste determination

Caste differentiation of honey bees (Apis mellifera) is a prime example of developmental plasticity, wherein identical genotypes yield either long-lived, reproductive queens or short-lived, facultatively sterile workers, influenced by larval diet. Beyond environmental factors, intragenomic conflict between genes inherited from the mother (matrigenes) versus the father (patrigenes) is also hypothesized to generate this plasticity. In honey bees, the Kinship Theory of Intragenomic Conflict predicts selection on patrigenes to enhance traits that result in direct fitness gained through reproduction, and thus patrigenes should favor the queen caste fate. Here, we conducted allele-specific transcriptome analyses on queen-destined larvae (QL) and worker-destined larvae (WL) at 192 hours post-fertilization (hpf), a critical stage for caste determination, in addition to 24hpf diploid eggs. Previous studies demonstrated that DNA methylation, the canonical epigenetic mechanism underlying transcriptional POEs in placental mammals, seed-bearing plants, and some insects, is not operating in honey bees or other social insect species. Here, we conducted allele-specific ChIP-seq analyses of H3K27me3, H3K4me3 and H3K27ac, to determine whether allelic variation in these histone post-translational modifications is associated with allelic variation in transcription.