Wu Mian-Zhi, Fan Shu-Ting, Zhang Yuan-Chen, Tan Jin-Fang, Zhu Guan-Heng
School of Agriculture and Biotechnology, Shenzhen Campus of Sun Yat-sen University, Shenzhen, China.
State Key Laboratory of Biocontrol, School of Agriculture and Biotechnology, Sun Yat-sen University, Shenzhen, China.
Front Physiol. 2024 Dec 11;15:1502753. doi: 10.3389/fphys.2024.1502753. eCollection 2024.
The juvenile hormone (JH) and 20-hydroxyecdysone (20E) are the central regulating hormones of insect development. The timing of their secretion usually leads to developmental transitions.
The developmental transitions were evaluated via the starvation treatment and the expressions of two key metamorphosis inducing factor in . Then, the main endocrine organs, including the brain-corpora cardiacum-corpora allatum and prothoracic gland, were sampled from L4-24 h and L6-24 h larvae for the RNA-seq analysis. Additionally, the critical rate-limiting enzyme of 20E synthesis, , was knocked down to mimic the downregulation of 20E synthesis in the late larval instar.
The critical weight (CW), when JH titer declines for metamorphosis, was determined be approximately L6-24 h in . However, the expression of the pupal specifier and the potential "metamorphosis initiation factor" showed a stepwise increase between L4-24 h and L6-24 h, suggesting that the developmental transitions may occur earlier. The RNA-seq analysis revealed that both 20E and JH synthesis enzymes were downregulated at the CW. In addition, strong tendencies in the expression pattern were detected among the lists of transcripts. Further knockdown of shadow induced larval development arrest and subsequent mortality, indicating that disrupting 20E synthesis before the CW is lethal. Besides, JH synthesis enzyme was down-regulated.
The downregulation of 20E synthesis enzymes at the CW may represent a carefully regulated event, suggesting a deceleration of larval growth and the initiation of some underlying physiological changes to set the stage for metamorphosis.
保幼激素（JH）和20-羟基蜕皮酮（20E）是昆虫发育的核心调节激素。它们的分泌时间通常会导致发育转变。
通过饥饿处理评估发育转变，并检测两种关键变态诱导因子的表达。然后，从L4-24小时和L6-24小时的幼虫中采集主要内分泌器官，包括脑-咽侧体-前胸腺，进行RNA测序分析。此外，敲低20E合成的关键限速酶，以模拟幼虫后期20E合成的下调。
在[具体昆虫名称]中，确定JH滴度下降以进行变态时的临界体重（CW）约为L6-24小时。然而，蛹特异性因子[具体名称]和潜在的“变态起始因子”[具体名称]的表达在L4-24小时和L6-24小时之间呈逐步增加，表明发育转变可能更早发生。RNA测序分析表明，在临界体重时，20E和JH合成酶均下调。此外，在转录本列表中检测到表达模式的强烈趋势。进一步敲低shadow导致幼虫发育停滞并随后死亡，表明在临界体重之前破坏20E合成是致命的。此外，JH合成酶也被下调。
在临界体重时20E合成酶的下调可能是一个经过精心调节的事件，表明幼虫生长减速，并开始一些潜在的生理变化，为变态奠定基础。
