Malka Osnat, Karunker Iris, Yeheskel Adva, Morin Shai, Hefetz Abraham
Department of Zoology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Israel.
FEBS J. 2009 Oct;276(19):5481-90. doi: 10.1111/j.1742-4658.2009.07232.x. Epub 2009 Aug 21.
The advances in honeybee sociogenomics have paved the way for the study of social communication processes at the gene level, in particular the expression of caste-specific pheromones. The queen honeybee mandibular pheromone provides an excellent model system, in that biosynthesis of the hydroxylating fatty acid caste-specific pheromone appears to be reduced to a single chemical hydroxylation step of stearic acid. Queens are typified by omega-1-hydroxylation, as opposed to the worker-typical omega-hydroxylation. We hypothesized that this bifurcation is the consequence of differential expression of caste-specific genes that code for fatty acid-hydroxylating enzymes from the cytochrome P450 (CYP) family. Bioinformatics studies disclosed two candidate proteins CYP4AA1 and CYP18A1. We thus investigated the expression of these genes in the mandibular glands of queens, and of queenright (QR) and queenless (QL) workers. The real-time PCR results revealed that CYP4AA1 (omega-hydroxylation) was expressed at high levels in both QR and QL workers, whereas in queens its expression was negligible. The expression of CYP18A1 (omega-1-hydroxylation), on the other hand, was high in the queen's glands and negligible in those of QR workers. In QL workers, however, the expression of CYP18A1 was considerably elevated and significantly greater than in QR workers. Three-dimensional structural models constructed for these enzymes demonstrate differences in the active site between CYP18A1 and CYP4AA1, in line with their differential catalytic specificity. The fact that queen pheromone plasticity can be tracked all the way to gene expression provides a new insight into the process of caste differentiation and the accompanying social communication.
蜜蜂社会基因组学的进展为在基因水平上研究社会交流过程，尤其是特定蜂型信息素的表达，铺平了道路。蜂王下颚信息素提供了一个出色的模型系统，因为羟基化脂肪酸特定蜂型信息素的生物合成似乎简化为硬脂酸的单一化学羟基化步骤。蜂王的典型特征是ω-1-羟基化，这与工蜂典型的ω-羟基化形成对比。我们推测这种分歧是细胞色素P450（CYP）家族中编码脂肪酸羟基化酶的特定蜂型基因差异表达的结果。生物信息学研究揭示了两种候选蛋白CYP4AA1和CYP18A1。因此，我们研究了这些基因在蜂王、有蜂王（QR）和无蜂王（QL）工蜂的下颚腺中的表达。实时PCR结果显示，CYP4AA1（ω-羟基化）在QR和QL工蜂中均高水平表达，而在蜂王中其表达可忽略不计。另一方面，CYP18A1（ω-1-羟基化）在蜂王腺体中表达高，在QR工蜂腺体中可忽略不计。然而，在QL工蜂中，CYP18A1的表达显著升高且明显高于QR工蜂。为这些酶构建的三维结构模型表明，CYP18A1和CYP4AA1的活性位点存在差异，这与其不同的催化特异性一致。蜂王信息素可塑性可一直追溯到基因表达这一事实，为蜂型分化过程及伴随的社会交流提供了新的见解。
