Department of Biology, Earlham College, Richmond, Indiana, United States of America.
PLoS One. 2012;7(8):e42433. doi: 10.1371/journal.pone.0042433. Epub 2012 Aug 3.
DNA methylation is a common regulator of gene expression, including acting as a regulator of developmental events and behavioral changes in adults. Using the unique system of genetic caste determination in Pogonomyrmex barbatus, we were able to document changes in DNA methylation during development, and also across both ancient and contemporary hybridization events.
METHODOLOGY/PRINCIPAL FINDINGS: Sodium bisulfite sequencing demonstrated in vivo methylation of symmetric CG dinucleotides in P. barbatus. We also found methylation of non-CpG sequences. This validated two bioinformatics methods for predicting gene methylation, the bias in observed to expected ratio of CpG dinucleotides and the density of CpG/TpG single nucleotide polymorphisms (SNP). Frequencies of genomic DNA methylation were determined for different developmental stages and castes using ms-AFLP assays. The genetic caste determination system (GCD) is probably the product of an ancestral hybridization event between P. barbatus and P. rugosus. Two lineages obligately co-occur within a GCD population, and queens are derived from intra-lineage matings whereas workers are produced from inter-lineage matings. Relative DNA methylation levels of queens and workers from GCD lineages (contemporary hybrids) were not significantly different until adulthood. Virgin queens had significantly higher relative levels of DNA methylation compared to workers. Worker DNA methylation did not vary among developmental stages within each lineage, but was significantly different between the currently hybridizing lineages. Finally, workers of the two genetic caste determination lineages had half as many methylated cytosines as workers from the putative parental species, which have environmental caste determination.
CONCLUSIONS/SIGNIFICANCE: These results suggest that DNA methylation may be a conserved regulatory mechanism moderating division of labor in both bees and ants. Current and historic hybridization appear to have altered genomic methylation levels suggesting a possible link between changes in overall DNA methylation and the origin and regulation of genetic caste determination in P. barbatus.
DNA 甲基化是一种常见的基因表达调控方式，包括作为成年期发育事件和行为变化的调节剂。利用 Pogonomyrmex barbatus 独特的遗传等级决定系统，我们能够记录发育过程中以及在古老和当代杂交事件中 DNA 甲基化的变化。
方法/主要发现：亚硫酸氢盐测序显示，P. barbatus 中存在对称 CG 二核苷酸的体内甲基化。我们还发现了非 CpG 序列的甲基化。这验证了两种预测基因甲基化的生物信息学方法，即观察到的 CpG 二核苷酸与预期的比值偏倚和 CpG/TpG 单核苷酸多态性 (SNP) 的密度。使用 ms-AFLP 分析确定了不同发育阶段和等级的基因组 DNA 甲基化频率。遗传等级决定系统 (GCD) 可能是 P. barbatus 和 P. rugosus 之间祖先杂交事件的产物。两个谱系在 GCD 种群中必然共同存在，蚁后是由谱系内交配产生的，而工蚁是由谱系间交配产生的。GCD 谱系（当代杂种）的蚁后和工蚁的相对 DNA 甲基化水平在成年前没有显著差异。处女蚁后与工蚁相比具有显著更高的相对 DNA 甲基化水平。在每个谱系内，工蚁的 DNA 甲基化在发育阶段之间没有变化，但在当前杂交的谱系之间有显著差异。最后，两个遗传等级决定谱系的工蚁的甲基化胞嘧啶数量是具有环境等级决定的假定亲种工蚁的一半。
结论/意义：这些结果表明，DNA 甲基化可能是调节蜜蜂和蚂蚁分工的保守调节机制。当前和历史杂交似乎改变了基因组甲基化水平，这表明在 P. barbatus 中，总 DNA 甲基化的变化与遗传等级决定的起源和调节之间可能存在联系。
