The Institute of Sericulture and Systems Biology, Southwest University, Chongqing 400715, China.
Insect Biochem Mol Biol. 2012 Dec;42(12):935-45. doi: 10.1016/j.ibmb.2012.09.006. Epub 2012 Sep 25.
The glucose-methanol-choline (GMC) oxidoreductases constitute a large gene family in insects. Some of these enzymes play roles in developmental or physiological process, such as ecdysteroid metabolism. However, little is known about the functional diversity of the insect GMC family. Here, we identified 43 GMC genes in the silkworm genome, the largest number of GMC genes among all the insect genomes sequenced to date. Similar to the other insects, there is a highly conserved GMC cluster within the second intron of the silkworm flotillin-2 (flo-2) gene. However, the silkworm GMC genes outside of the conserved GMC cluster have experienced a large expansion. Phylogenetic analysis suggested that the silkworm GMCβ subfamily contained 22 copies and made a major contribution to expansion of the silkworm GMC genes. Eighteen of the 22 members of the silkworm GMCβ subfamily are located outside of the conserved GMC cluster, and are known as silkworm expansion genes (SEs). Relative-rate tests showed that SEs evolved significantly faster than the GMCβ genes inside the conserved GMC cluster. Accordingly, the third position GC content (GC3s) and codon bias of SEs are significantly different from those of the GMCβ genes in the conserved GMC cluster. The elevated evolutionary rate of the silkworm GMCβ genes outside of the conserved GMC cluster may reflect the evolution of function diversity. At least 24 of the 43 silkworm GMC genes were differently transcribed and expressed in a tissue- or stage-specific manner during the larval stage. Strikingly, microarray data revealed that four different pathogens upregulated most of the silkworm GMCβ genes. Furthermore, RNA interference of representative upregulated GMCβ genes reduced the survival rate of the silkworm when infected by pathogens. Taken together, the results suggested that expansion of the silkworm GMC oxidoreductase genes is associated with immunity.
葡萄糖-甲醇-胆碱（GMC）氧化还原酶构成了昆虫中一个庞大的基因家族。其中一些酶在发育或生理过程中发挥作用，如蜕皮激素代谢。然而，关于昆虫 GMC 家族的功能多样性知之甚少。在这里，我们在蚕基因组中鉴定了 43 个 GMC 基因，这是迄今为止测序的所有昆虫基因组中 GMC 基因数量最多的。与其他昆虫相似，在蚕的 flotillin-2（flo-2）基因的第二个内含子中存在一个高度保守的 GMC 簇。然而，蚕的 GMC 基因在保守的 GMC 簇之外经历了大量扩张。系统发育分析表明，蚕 GMCβ 亚家族包含 22 个拷贝，对蚕 GMC 基因的扩张做出了主要贡献。蚕 GMCβ 亚家族的 22 个成员中的 18 个位于保守的 GMC 簇之外，被称为蚕扩张基因（SEs）。相对速率检验表明，SEs 的进化速度明显快于保守的 GMC 簇内的 GMCβ 基因。因此，SEs 的第三位 GC 含量（GC3s）和密码子偏好与保守的 GMC 簇内的 GMCβ 基因明显不同。蚕 GMCβ 基因在保守的 GMC 簇之外的进化速度升高可能反映了功能多样性的进化。在幼虫阶段，至少有 43 个蚕 GMC 基因中的 24 个以组织或阶段特异性的方式转录和表达。引人注目的是，微阵列数据显示，四种不同的病原体上调了大多数蚕 GMCβ 基因。此外，代表性上调的 GMCβ 基因的 RNA 干扰降低了蚕在感染病原体时的存活率。总之，结果表明蚕 GMC 氧化还原酶基因的扩张与免疫有关。
