Philipps-Universität Marburg, Institut für Pharmazeutische Chemie, Marbacher Weg 6, Marburg, 35032, Germany.
Julius-Maximilians-Universität Würzburg, Verhaltensphysiologie und Soziobiologie, Am Hubland, Würzburg, 97074, Germany.
BMC Genomics. 2019 Jan 25;20(1):88. doi: 10.1186/s12864-018-5402-6.
The honeybee (Apis mellifera) represents a model organism for social insects displaying behavioral plasticity. This is reflected by an age-dependent task allocation. The most protruding tasks are performed by young nurse bees and older forager bees that take care of the brood inside the hive and collect food from outside the hive, respectively. The molecular mechanism leading to the transition from nurse bees to foragers is currently under intense research. Circular RNAs, however, were not considered in this context so far. As of today, this group of non-coding RNAs was only known to exist in two other insects, Drosophila melanogaster and Bombyx mori. Here we complement the state of circular RNA research with the first characterization in a social insect.
We identified numerous circular RNAs in the brain of A. mellifera nurse bees and forager bees using RNA-Seq with exonuclease enrichment. Presence and circularity were verified for the most abundant representatives. Back-splicing in honeybee occurs further towards the end of transcripts and in transcripts with a high number of exons. The occurrence of circularized exons is correlated with length and CpG-content of their flanking introns. The latter coincides with increased DNA-methylation in the respective loci. For two prominent circular RNAs the abundance in worker bee brains was quantified in TaqMan assays. In line with previous findings of circular RNAs in Drosophila, circAmrsmep2 accumulates with increasing age of the insect. In contrast, the levels of circAmrad appear age-independent and correlate with the bee's task. Its parental gene is related to amnesia-resistant memory.
We provide the first characterization of circRNAs in a social insect. Many of the RNAs identified here show homologies to circular RNAs found in Drosophila and Bombyx, indicating that circular RNAs are a common feature among insects. We find that exon circularization is correlated to DNA-methylation at the flanking introns. The levels of circAmrad suggest a task-dependent abundance that is decoupled from age. Moreover, a GO term analysis shows an enrichment of task-related functions. We conclude that circular RNAs could be relevant for task allocation in honeybee and should be investigated further in this context.
蜜蜂（Apis mellifera）是一种具有行为可塑性的社会性昆虫模式生物。这种可塑性表现在其年龄依赖性的任务分配上。最突出的任务由年轻的内勤蜂和年长的外勤蜂完成，内勤蜂照顾蜂巢内的幼虫，外勤蜂则从蜂巢外采集食物。导致内勤蜂向外勤蜂转变的分子机制目前正在深入研究中。然而，到目前为止，在这方面还没有考虑环状 RNA。截至今天，人们只知道这类非编码 RNA 还存在于另外两种昆虫——黑腹果蝇（Drosophila melanogaster）和家蚕（Bombyx mori）中。在这里，我们用 RNA-Seq 结合外切酶富集法在社会性昆虫中首次对环状 RNA 进行了描述。
我们在内勤蜂和外勤蜂的大脑中使用 RNA-Seq 结合外切酶富集法鉴定了大量的环状 RNA。对最丰富的代表进行了存在和环状的验证。在蜜蜂中，RNA 的反向剪接发生在转录本的末端，并且在具有多个外显子的转录本中发生。环状外显子的发生与它们侧翼内含子的长度和 CpG 含量相关。后者与相应基因座中 DNA 甲基化的增加相一致。对于两个突出的环状 RNA，我们使用 TaqMan 检测法在工蜂大脑中对其丰度进行了定量。与之前在果蝇中发现的环状 RNA 一致，circAmrsmep2 的丰度随着昆虫年龄的增加而增加。相比之下，circAmrad 的水平与年龄无关，与蜜蜂的任务相关。其母体基因与抗遗忘记忆有关。
我们首次对社会性昆虫中的环状 RNA 进行了描述。这里鉴定的许多 RNA 与在果蝇和家蚕中发现的环状 RNA 具有同源性，这表明环状 RNA 是昆虫的一个共同特征。我们发现外显子的环化与侧翼内含子的 DNA 甲基化相关。circAmrad 的水平表明其丰度与任务相关，与年龄无关。此外，GO 术语分析显示与任务相关的功能富集。我们得出结论，环状 RNA 可能与蜜蜂的任务分配有关，在这方面应该进一步研究。
