Guangdong Provincial Key Laboratory of Biotechnology for Plant Development, School of Life Sciences, South China Normal University, Guangzhou, China.
Insect Sci. 2014 Aug;21(4):449-58. doi: 10.1111/1744-7917.12055. Epub 2013 Oct 2.
Insect midgut secretes a semi-permeable peritrophic membrane (PM), which plays important roles in protecting the midgut and helping with food digestion. The lepidopteran larvae produce type 1 PM, which is degraded when insects develop into the metamorphic stages. However, the underlying mechanism is unclear. In the present study, two peritrophin-like proteins (peritrophin-57 and 37) were identified from the midgut expression sequence tag library and transcriptome of the common cutworm, Spodoptera litura. The temporal and spatial expression patterns and responses to the induction of 20-hydroxyecdysone (20E) and starvation were examined by real-time quantitative polymerase chain reaction according to their common sequence region. The chitin-binding activity was also studied using a competitor, calcofluor. The open reading frames are 1 554 and 1 020 bp, respectively. They shared four highly conserved peritrophin-A domains and were expressed only in the midgut rather than in the other tissues, including fat body, epidermis, Malpighian tube and hemolymph. Their transcriptional expression could only be detected at the larval stages rather than in eggs, prepupae, pupae and adults. The purified protein of peritrophin-37 bound to chitin in a dose-dependent manner. These results indicate that the two proteins are peritrophins, the structural components of PM. In addition, the messenger RNA levels of the two peritrophins were significantly down-regulated by 20E injection, whereas feeding/starvation had no effect on the expression. These findings suggest that the increase of 20E titer may be an important factor which controls the degradation of PM during metamorphosis.
昆虫中肠分泌一种半透性围食膜（PM），它在保护中肠和帮助食物消化方面起着重要作用。鳞翅目幼虫产生 1 型 PM，当昆虫发育到变态阶段时，PM 会被降解。然而，其潜在机制尚不清楚。本研究从粘虫 Spodoptera litura 中肠表达序列标签文库和转录组中鉴定出两种围食膜蛋白（peritrophin-57 和 37）。根据其共同的序列区域，通过实时定量聚合酶链反应检测其时空表达模式以及对 20-羟基蜕皮酮（20E）和饥饿的诱导反应。还使用竞争物 Calcofluor 研究了几丁质结合活性。开放阅读框分别为 1554 和 1020bp，它们共享四个高度保守的围食膜 A 结构域，仅在中肠表达，而不在其他组织（包括脂肪体、表皮、马氏管和血液）中表达。它们的转录表达只能在幼虫阶段检测到，而不能在卵、预蛹、蛹和成虫中检测到。纯化的 peritrophin-37 蛋白与几丁质呈剂量依赖性结合。这些结果表明，这两种蛋白是围食膜的结构成分——围食膜蛋白。此外，20E 注射显著下调了两种围食膜蛋白的信使 RNA 水平，而摄食/饥饿对其表达没有影响。这些发现表明，20E 浓度的增加可能是控制变态过程中 PM 降解的一个重要因素。
