Department of Applied Biology, School of Biology and Basic Medical Sciences, Medical College, Soochow University, Suzhou, China; National Engineering Laboratory for Modern Silk, Institute of Agricultural Biotechnology & Ecology, Soochow University, Suzhou, China.
Arch Insect Biochem Physiol. 2014 Jan;85(1):36-47. doi: 10.1002/arch.21141. Epub 2013 Dec 13.
Chitin synthase (CHS) is the key regulatory enzyme in chitin synthesis and excretion in insects, and a specific target of insecticides. We cloned a CHS B gene of Bombyx mori (BmChsB) and showed it to be midgut specific, highly expressed during the feeding process in the larva. Knockdown of BmChsB expression in the third-instar larvae increased the number of nonmolting and abnormally molting larvae. Exposure to nikkomycin Z, a CHS inhibitor, reduced the amount of chitin in the peritrophic membrane of molted larvae, whereas abnormally elevated BmChsB mRNA levels were readily detected from the end of molting and in the newly molted larvae. Exogenous 20-hydroxyecdysone (20E) and methoprene, a juvenile hormone analogue, significantly upregulated the expression of BmChsB when the levels of endogenous molting hormone (MH) were low and the levels of endogenous juvenile hormone (JH) were high immediately after molting. When levels of endogenous MH were high and those of endogenous JH were low during the molting stage, exogenous 20E did not upregulate BmChsB expression and exogenous methoprene upregulated it negligibly. When the endogenous hormone levels were low during the mulberry-leaf intake process, BmChsB expression was upregulated by exogenous methoprene. We conclude that the expression of BmChsB is regulated by insect hormones, and directly affects the chitin-synthesis-dependent form of the peritrophic membrane and protects the food intake and molting process of silkworm larvae.
几丁质合酶（CHS）是昆虫中几丁质合成和排泄的关键调节酶，也是杀虫剂的特定靶标。我们克隆了家蚕（Bombyx mori）的 CHS B 基因（BmChsB），并证实其在幼虫取食过程中仅在中肠特异表达。在 3 龄幼虫中敲低 BmChsB 的表达会增加未蜕皮和异常蜕皮幼虫的数量。CHS 抑制剂 nikkomycin Z 处理蜕皮后的幼虫会降低其围食膜中的几丁质含量，而在蜕皮结束和刚蜕皮的幼虫中很容易检测到异常升高的 BmChsB mRNA 水平。蜕皮激素（20E）和保幼激素类似物甲氧普烯在 MH 水平低而 JH 水平高时显著上调 BmChsB 的表达，此时内源蜕皮激素（MH）和内源性保幼激素（JH）水平高。在蜕皮阶段 MH 水平高而 JH 水平低时，外源 20E 不会上调 BmChsB 的表达，而外源甲氧普烯则可轻微上调其表达。当在桑叶取食过程中内源激素水平较低时，外源甲氧普烯会上调 BmChsB 的表达。我们得出结论，BmChsB 的表达受昆虫激素调控，直接影响依赖于几丁质合成的围食膜的形成，并保护家蚕幼虫的取食和蜕皮过程。
