Graduate School of Bio-Agricultural Sciences, Nagoya University, Nagoya, Japan.
Faculty of Life and Environmental Science, Shimane University, Matsue, Japan.
PLoS One. 2020 Apr 13;15(4):e0231451. doi: 10.1371/journal.pone.0231451. eCollection 2020.
Insect molting hormone (ecdysteroids) and juvenile hormone regulate molting and metamorphic events in a variety of insect species. Mealybugs undergo sexually dimorphic metamorphosis: males develop into winged adults through non-feeding, pupa-like stages called prepupa and pupa, while females emerge as neotenic wingless adults. We previously demonstrated, in the Japanese mealybug Planococcus kraunhiae (Kuwana), that the juvenile hormone titer is higher in males than in females at the end of the juvenile stage, which suggests that juvenile hormone may regulate male-specific adult morphogenesis. Here, we examined the involvement of ecdysteroids in sexually dimorphic metamorphosis. To estimate ecdysteroid titers, quantitative RT-PCR analyses of four Halloween genes encoding for cytochrome P450 monooxygenases in ecdysteroid biosynthesis, i.e., spook, disembodied, shadow and shade, were performed. Overall, their expression levels peaked before each nymphal molt. Transcript levels of spook, disembodied and shadow, genes that catalyze the steps in ecdysteroid biosynthesis in the prothoracic gland, were higher in males from the middle of the second nymphal instar to adult emergence. In contrast, the expression of shade, which was reported to be involved in the conversion of ecdysone into 20-hydroxyecdysone in peripheral tissues, was similar between males and females. These results suggest that ecdysteroid biosynthesis in the prothoracic gland is more active in males than in females, although the final conversion into 20-hydroxyecdysone occurs at similar levels in both sexes. Moreover, expression profiles of ecdysone response genes, ecdysone receptor and ecdysone-induced protein 75B, were also analyzed. Based on these expression profiles, we propose that the changes in ecdysteroid titer differ between males and females, and that high ecdysteroid titer is essential for directing male adult development.
昆虫蜕皮激素（蜕皮激素）和保幼激素调节各种昆虫物种的蜕皮和变态事件。粉虱经历性二态变态：雄性通过非摄食、类似蛹的预蛹和蛹阶段发育成有翅成虫，而雌性则发育成无翅的幼态成虫。我们之前在日本粉虱 Planococcus kraunhiae（Kuwana）中证明，在幼期结束时，雄性的保幼激素滴度高于雌性，这表明保幼激素可能调节雄性特有的成虫形态发生。在这里，我们研究了蜕皮激素在性二态变态中的作用。为了估计蜕皮激素滴度，我们对编码蜕皮激素生物合成中细胞色素 P450 单加氧酶的四个万圣节基因（spook、disembodied、shadow 和 shade）进行了定量 RT-PCR 分析，即 spook、disembodied、shadow 和 shade。总的来说，它们的表达水平在每次若虫蜕皮前达到峰值。参与前胸腺蜕皮激素生物合成步骤的 spook、disembodied 和 shadow 基因的转录水平在第二龄中期至成虫出现的雄性中较高。相比之下， shade 的表达水平在雄性和雌性之间相似，该基因被报道参与外周组织中蜕皮酮向 20-羟基蜕皮酮的转化。这些结果表明，尽管最终转化为 20-羟基蜕皮酮在两性中发生的水平相似，但雄性前胸腺的蜕皮激素生物合成比雌性更活跃。此外，还分析了蜕皮激素反应基因、蜕皮激素受体和蜕皮激素诱导蛋白 75B 的表达谱。基于这些表达谱，我们提出了雌雄两性蜕皮激素滴度的变化不同，并且高蜕皮激素滴度对于指导雄性成虫发育是必要的。
