Importance of juvenile hormone signaling arises with competence of insect larvae to metamorphose
Importance of juvenile hormone signaling arises with competence of insect larvae to metamorphose
复制标题
DOI：
10.1016/j.ydbio.2014.03.006
复制
发表时间：
2014-06-15
影响因子：
2.7
通讯作者：
Jindra, Marek
中科院分区：
文献类型：
--
作者：
Smykal, Viastimil;Daimon, Takaaki;Jindra, Marek
保幼激素(JH)延缓昆虫幼虫的变态，直到其达到合适的阶段和大小。然后，在最终幼虫龄期，JH分泌的下降允许变态蜕皮，将幼虫直接(半代谢)或通过蛹阶段(全代谢)转化为成虫。在这两种情况下，JH通过JH受体Met激活Kr-H1基因来阻止变态。甲硫氨酸、Kr-H1或JH的去除本身会触发有害的早熟变性。虽然JH被认为在整个幼虫生命周期中保持幼虫状态，但各种耗尽JH的方法都未能诱导早龄幼虫变态。为了确定JH信号何时成为防止早熟变态的重要因素，我们选择了半变态的金龟子和全变态的家蚕。这两个物种都经历了固定数量的五龄幼虫。在RNAi介导的Met或Kr-H1基因的敲除下，在第4龄(倒数第二龄)期间处理的梨树幼虫出现了早熟发育，但年轻的幼虫对这两个基因的缺失表现出越来越强的抵抗力。发育早熟变态轻微体征的最早龄期为第3龄。因此，JH反应基因可能不需要在前两个幼虫龄期维持幼虫程序。接下来，我们研究了不能合成正宗的环氧化形式的JH的家蚕mod突变体。虽然MOD幼虫自孵化以来Kr-H1mRNA的表达水平严重下降，但它们只有在4龄后才进入变态，很少在3龄后进入变态。根据在梨属和家蚕中的发现，我们认为昆虫的胚胎后发育最初是独立于JH的。只有后来，当幼虫获得进入变态的能力时，JH信号才成为必要的，以防止早熟变态和优化生长。(C)2014 Elsevier Inc.保留所有权利。
Juvenile hormone (JH) postpones metamorphosis of insect larvae until they have attained an appropriate stage and size. Then, during the final larval instar, a drop in JH secretion permits a metamorphic molt that transforms larvae to adults either directly (hemimetaboly) or via a pupal stage (holometaboly). In both scenarios, JH precludes metamorphosis by activating the Kr-h1 gene through a JH receptor, Methoprene-tolerant (Met). Removal of Met, Kr-h1, or JH itself triggers deleterious precocious metamorphosis. Although JH is thought to maintain the juvenile status throughout larval life, various methods of depleting JH failed to induce metamorphosis in early-instar larvae. To determine when does JH signaling become important for the prevention of precocious metamorphosis, we chose the hemimetabolous bug, Pyrrhocoris apterus, and the holometabolous silkworm, Bombyx moo. Both species undergo a fixed number of five larval instars. Pyrrhocoris larvae subjected to RNAi-mediated knockdown of Met or Kr-h1 underwent precocious adult development when treated during the fourth (penultimate) instar, but younger larvae proved increasingly resistant to loss of either gene. The earliest instar developing minor signs of precocious metamorphosis was the third. Therefore, the JH-response genes may not be required to maintain the larval program during the first two larval instars. Next, we examined Bombyx mod mutants that cannot synthesize authentic, epoxidized forms of JH. Although mod larvae expressed Kr-h1 mRNA at severely reduced levels since hatching, they only entered metamorphosis by pupating after four, rarely three instars. Based on findings in Pyrrhocoris and Bombyx, we propose that insect postembryonic development is initially independent of JH. Only later, when larvae gain competence to enter metamorphosis, JH signaling becomes necessary to prevent precocious metamorphosis and to optimize growth. (C) 2014 Elsevier Inc. All rights reserved.