Geiser Dawn L, Chavez Carrie A, Flores-Munguia Roberto, Winzerling Joy J, Pham Daphne Q-D
College of Agriculture and Life Sciences, The University of Arizona, Tucson, AZ, USA.
Eur J Biochem. 2003 Sep;270(18):3667-74. doi: 10.1046/j.1432-1033.2003.03709.x.
Diseases transmitted by hematophagous (blood-feeding) insects are responsible for millions of human deaths worldwide. In hematophagous insects, the blood meal is important for regulating egg maturation. Although a high concentration of iron is toxic for most organisms, hematophagous insects seem unaffected by the iron load in a blood meal. One means by which hematophagous insects handle this iron load is, perhaps, by the expression of iron-binding proteins, specifically the iron storage protein ferritin. In vertebrates, ferritin is an oligomer composed of two types of subunits called heavy and light chains, and is part of the constitutive antioxidant response. Previously, we found that the insect midgut, a main site of iron load, is also a primary site of ferritin expression and that, in the yellow fever mosquito, Aedes aegypti, the expression of the ferritin heavy-chain homologue (HCH) is induced following blood feeding. We now show that the expression of the Aedes ferritin light-chain homologue (LCH) is also induced with blood-feeding, and that the genes of the LCH and HCH are tightly clustered. mRNA levels for both LCH- and HCH-genes increase with iron, H2O2 and hemin treatment, and the temporal expression of the genes is very similar. These results confirm that ferritin could serve as the cytotoxic protector in mosquitoes against the oxidative challenge of the bloodmeal. Finally, although the Aedes LCH has no iron responsive element (IRE) at its 5'-untranslated region (UTR), the 5'-UTR contains several introns that are alternatively spliced, and this alternative splicing event is different from any ferritin message seen to date.
吸血昆虫传播的疾病在全球导致数百万人死亡。在吸血昆虫中，血餐对调节卵子成熟很重要。尽管高浓度的铁对大多数生物有毒，但吸血昆虫似乎不受血餐中铁负荷的影响。吸血昆虫处理这种铁负荷的一种方式可能是通过表达铁结合蛋白，特别是铁储存蛋白铁蛋白。在脊椎动物中，铁蛋白是一种由重链和轻链两种亚基组成的寡聚体，是组成性抗氧化反应的一部分。此前，我们发现昆虫中肠是铁负荷的主要部位，也是铁蛋白表达的主要部位，并且在黄热病蚊子埃及伊蚊中，吸血后铁蛋白重链同源物（HCH）的表达会被诱导。我们现在表明，埃及伊蚊铁蛋白轻链同源物（LCH）的表达在吸血后也会被诱导，并且LCH和HCH的基因紧密聚集。LCH基因和HCH基因的mRNA水平在铁、过氧化氢和血红素处理后都会增加，并且这些基因的时间表达非常相似。这些结果证实铁蛋白可以作为蚊子对抗血餐氧化挑战的细胞毒性保护剂。最后，尽管埃及伊蚊LCH在其5'非翻译区（UTR）没有铁反应元件（IRE），但其5'UTR包含几个可变剪接的内含子，并且这种可变剪接事件与迄今为止所见的任何铁蛋白信息都不同。
