Genetic diversity among queen bee, worker bees and larvae in terms of retrotransposon movements

Objective Honeybee (Apis mellifera L.) is a model organism, contributing significant effect on global ecology by pollination and examining due to its social behaviour. Methods In this study, barley-specific Sukkula and Nikita retrotransposons were analysed using IRAP (Inter-Retrotransposon Amplification Polymorphism) marker technique, and the relationships between retrotransposon movements and development were also investigated in three different colonies of the Caucasian bee (Apis mellifera caucasica). Furthermore, transposon sequences belonging to Apis mellifera, Bombus terrestris, Triticum turgidum and Hordeum vulgare were also examined to figure out evolutionary relationships. Results For this purpose, a queen bee, five worker bees, and five larvae from each colony were studied. Both retrotransposons were found in all samples in three colonies with different polymorphism ratios (0-100% for Nikita and 0-67% for Sukkula). We also determined polymorphisms in queen-worker (0-83% for Nikita, 0-63% for Sukkula), queen-larvae (0-83% for Nikita, 0-43% for Sukkula) and worker-larvae comparisons (0-100% for Nikita, 0-63% for Sukkula) in colonies. Moreover, close relationships among transposons found in plant and insect genomes as a result of in silico evaluations to verify experimental results. Conclusion This work could be one of the first studies to analyse plant-specific retrotransposons’ movements in honeybee genome. Results are expected to understand evolutionary relationships in terms of horizontal transfer of transposons among kingdoms.

Tools and applications for integrative analysis of DNA methylation in social insects

DNA methylation is a common epigenetic signaling tool and an important biological process which is widely studied in a large array of species. The presence, level, and function of DNA methylation varies greatly across species. In insects, DNA methylation systems are reduced, and methylation rates are often low. Low methylation levels probed by whole genome bisulfite sequencing require great care with respect to data quality control and intepretation. Here we introduce BWASP/R, a reproducible, scalable workflow, that allows efficient, scalable, and entirely reproducible analyses of raw DNA methylation sequencing data. Consistent application of quality control filters and analysis parameters provides fair comparisons among different studies and an integrated view of all experiments on one species. We describe the capabilities of the BWASP/R workflow by re-analyzing several publicly available social insect WGBS datasets, comprising 70 samples and cumulatively 147 replicates from four different species. We show that the CpG methylome comprises only about 1.5% of CpG sites in the honeybee genome and that the cumulative data are consistent with genetic signatures of site accessibility and physiological control of methylation levels.Significance StatementDNA methylation in the honeybee genome occurs almost entirely at CpG sites. Methylation rates are small compared to rates in mammalian or plant genomes. De novo analysis of all published honeybee methylation studies and statistical modeling suggests that the CpG methylome consists of about only 300,000 sites. The development of a fully reproducible, scalable, portable workflow allows for easy accessible updates of integrative views of all current experiments. The integrated results for the honeybee are consistent with genetic determination of methylation site accessibility by yet uncharacterized sequence features and physiological control of methylation levels at those sites.

Genome Architecture Facilitates Phenotypic Plasticity in the Honeybee (Apis mellifera)

Phenotypic plasticity, the ability of an organism to alter its phenotype in response to an environmental cue, facilitates rapid adaptation to changing environments. Plastic changes in morphology and behavior are underpinned by widespread gene expression changes. However, it is unknown if, or how, genomes are structured to ensure these robust responses. Here, we use repression of honeybee worker ovaries as a model of plasticity. We show that the honeybee genome is structured with respect to plasticity; genes that respond to an environmental trigger are colocated in the honeybee genome in a series of gene clusters, many of which have been assembled in the last 80 My during the evolution of the Apidae. These clusters are marked by histone modifications that prefigure the gene expression changes that occur as the ovary activates, suggesting that these genomic regions are poised to respond plastically. That the linear sequence of the honeybee genome is organized to coordinate widespread gene expression changes in response to environmental influences and that the chromatin organization in these regions is prefigured to respond to these influences is perhaps unexpected and has implications for other examples of plasticity in physiology, evolution, and human disease.

Detecting rare asymmetrically methylated cytosines and decoding methylation patterns in the honeybee genome

Context-dependent gene expression in eukaryotes is controlled by several mechanisms including cytosine methylation that primarily occurs in the CG dinucleotides (CpGs). However, less frequent non-CpG asymmetric methylation has been found in various cell types, such as mammalian neurons, and recent results suggest that these sites can repress transcription independently of CpG contexts. In addition, an emerging view is that CpG hemimethylation may arise not only from deregulation of cellular processes but also be a standard feature of the methylome. Here, we have applied a novel approach to examine whether asymmetric CpG methylation is present in a sparsely methylated genome of the honeybee, a social insect with a high level of epigenetically driven phenotypic plasticity. By combining strand-specific ultra-deep amplicon sequencing of illustrator genes with whole-genome methylomics and bioinformatics, we show that rare asymmetrically methylated CpGs can be unambiguously detected in the honeybee genome. Additionally, we confirm differential methylation between two phenotypically and reproductively distinct castes, queens and workers, and offer new insight into the heterogeneity of brain methylation patterns. In particular, we challenge the assumption that symmetrical methylation levels reflect symmetry in the underlying methylation patterns and conclude that hemimethylation may occur more frequently than indicated by methylation levels. Finally, we question the validity of a prior study in which most of cytosine methylation in this species was reported to be asymmetric.