Hodges Theresa K, Cosme Luciano V, Athrey Giridhar, Pathikonda Sharmila, Takken Willem, Slotman Michel A
Department of Entomology, Texas A&M University, College Station, TX 77843, USA.
BMC Genomics. 2014 Dec 11;15(1):1089. doi: 10.1186/1471-2164-15-1089.
The malaria mosquito Anopheles gambiae has a high preference for human hosts, a characteristic that contributes greatly to its capacity for transmitting human malaria. A sibling species, An. quadriannulatus, has a quite different host preference and feeds mostly on bovids. For this reason it does not contribute to human malaria transmission. Host seeking in mosquitoes is modulated by the olfactory system, which is primarily housed in the antennae and maxillary palps. Therefore, the detection of differing host odors by sibling species may be reflected in the expression level of the olfactory genes involved. Accordingly, we compared the transcriptomes of the antennae and maxillary palps of An. gambiae and An. quadriannulatus.
We identified seven relatively abundant olfactory receptors, nine ionotropic receptors and three odorant binding proteins that are substantially up-regulated in An. gambiae antennae. Interestingly, we find that the maxillary palps of An. gambiae contain a species-specific olfactory receptor, Or52, and five An. gambiae-specific gustatory receptors (AgGr48-52) that are relatively abundant. These five gustatory receptors are also expressed in An. gambiae antennae, although at lower level, indicating a likely role in olfaction, rather than gustation. We also document an approximately three-fold higher overall expression of olfaction genes in the maxillary palps of An. quadriannulatus, indicating an important role of this organ in the olfaction system of this species. Finally, the expression of the CO2 receptor genes is five to six-fold higher in the zoophilic An. quadriannulatus, implying a much higher sensitivity for detecting CO2.
These results identify potential human host preference genes in the malaria vector An. gambiae. Interestingly, species-specific expression of several gustatory receptors in the olfactory organs indicate a role in olfaction rather than gustation. Additionally, a more expansive role for maxillary palps in olfaction is implicated than previously thought, albeit more so in the zoophilic An. quadriannulatus.
冈比亚疟蚊对人类宿主有高度偏好，这一特性极大地促进了其传播人类疟疾的能力。其同胞物种四斑按蚊具有截然不同的宿主偏好，主要以牛科动物为食。因此，它不会传播人类疟疾。蚊子寻找宿主的行为受嗅觉系统调节，嗅觉系统主要位于触角和下颚须中。因此，同胞物种对不同宿主气味的检测可能反映在相关嗅觉基因的表达水平上。据此，我们比较了冈比亚按蚊和四斑按蚊触角和下颚须的转录组。
我们鉴定出七个相对丰富的嗅觉受体、九个离子型受体和三个气味结合蛋白，它们在冈比亚按蚊触角中大量上调。有趣的是，我们发现冈比亚按蚊的下颚须含有一种物种特异性嗅觉受体Or52，以及五个相对丰富的冈比亚按蚊特异性味觉受体（AgGr48 - 52）。这五个味觉受体在冈比亚按蚊触角中也有表达，尽管水平较低，这表明它们可能在嗅觉而非味觉中起作用。我们还记录到四斑按蚊下颚须中嗅觉基因的总体表达大约高出三倍，表明该器官在该物种嗅觉系统中起重要作用。最后，嗜动物的四斑按蚊中二氧化碳受体基因的表达高出五到六倍，这意味着其检测二氧化碳的敏感性要高得多。
这些结果鉴定出了疟蚊媒介冈比亚按蚊中潜在的人类宿主偏好基因。有趣的是，嗅觉器官中几种味觉受体的物种特异性表达表明它们在嗅觉而非味觉中起作用。此外，下颚须在嗅觉中的作用比之前认为的更广泛，尽管在嗜动物的四斑按蚊中更是如此。
