Department of Evolution, Systematics, and Ecology, The Alexander Silberman Institute of Life Sciences, Hebrew University of Jerusalem, Jerusalem, Israel.
BMC Evol Biol. 2010 Apr 30;10:120. doi: 10.1186/1471-2148-10-120.
Regulation of worker behavior by dominant queens or workers is a hallmark of insect societies, but the underlying molecular mechanisms and their evolutionary conservation are not well understood. Honey bee and bumble bee colonies consist of a single reproductive queen and facultatively sterile workers. The queens' influences on the workers are mediated largely via inhibition of juvenile hormone titers, which affect division of labor in honey bees and worker reproduction in bumble bees. Studies in honey bees identified a transcription factor, Krüppel-homolog 1 (Kr-h1), whose expression in worker brains is significantly downregulated in the presence of a queen or queen pheromone and higher in forager bees, making this gene an ideal candidate for examining the evolutionary conservation of socially regulated pathways in Hymenoptera.
In contrast to honey bees, bumble bees foragers do not have higher Kr-h1 levels relative to nurses: in one of three colonies levels were similar in nurses and foragers, and in two colonies levels were higher in nurses. Similarly to honey bees, brain Kr-h1 levels were significantly downregulated in the presence versus absence of a queen. Furthermore, in small queenless groups, Kr-h1 levels were downregulated in subordinate workers with undeveloped ovaries relative to dominant individuals with active ovaries. Brain Kr-h1 levels were upregulated by juvenile hormone treatment relative to a vehicle control. Finally, phylogenetic analysis indicates that KR-H1 orthologs are presence across insect orders. Though this protein is highly conserved between honey bees and bumble bees, there are significant differences between orthologs of insects from different orders.
Our results suggest that Kr-h1 is associated with juvenile hormone mediated regulation of reproduction in bumble bees. The expression of this transcription factor is inhibited by the queen and associated with endocrine mediated regulation of social organization in two species of bees. Thus, KR-H1 may transcriptionally regulate a conserved genetic module that is part of a pathway that has been co-opted to function in social behavior, and adjusts the behavior of workers to their social environmental context.
工蜂或蜂王对工蜂行为的调节是昆虫社会的一个显著特征，但相关的分子机制及其进化保守性尚不清楚。蜜蜂和熊蜂的群体由一个单一的生殖蜂王和可育的不育工蜂组成。蜂王对工蜂的影响主要通过抑制保幼激素滴度来实现，这影响了蜜蜂的劳动分工和熊蜂的工蜂繁殖。在蜜蜂中进行的研究确定了一个转录因子 Krüppel-homolog 1（Kr-h1），其在蜂王或蜂王信息素存在下，工蜂大脑中的表达显著下调，而在觅食蜂中表达更高，这使得该基因成为研究膜翅目动物中社会调节途径进化保守性的理想候选基因。
与蜜蜂不同的是，熊蜂觅食蜂的 Kr-h1 水平相对于看护蜂并没有更高：在三个群体中的一个中，看护蜂和觅食蜂的水平相似，而在另外两个群体中，水平更高的是看护蜂。与蜜蜂类似，在存在蜂王的情况下，大脑 Kr-h1 水平显著下调。此外，在没有蜂王的小群体中，未发育卵巢的从属工蜂的 Kr-h1 水平相对于卵巢活跃的支配个体下调。与载体对照相比，用保幼激素处理可使大脑 Kr-h1 水平上调。最后，系统发育分析表明，KR-H1 同源物存在于昆虫的各个目。尽管这种蛋白在蜜蜂和熊蜂之间高度保守，但不同目昆虫的同源物之间存在显著差异。
我们的结果表明，Kr-h1 与熊蜂中保幼激素介导的生殖调节有关。该转录因子的表达受蜂王抑制，并与两种蜜蜂的内分泌介导的社会组织调节有关。因此，KR-H1 可能转录调节一个保守的遗传模块，该模块是被共同作用于社会行为的途径的一部分，并调整工蜂的行为以适应其社会环境背景。
