BmCncC/keap1-pathway is involved in high-temperature induced metamorphosis regulation of silkworm,Bombyx mori
Authors: Li Jinxin , Mao Tingting , Lu Zhengting , Li Mengxue , Lu Zhengting , Qu Jianwei , Fang Yilong , Chen Jian , Wang Hui , Cheng Xiaoyu , Jiahuan Hu , Liu Yu , Ziyan Zhang , Zhiya Gu , Fanchi Li , Li Bing 
Published: November 2018

The global warming has affected the growth, development and reproduction of insects. However, the molecular mechanism of high temperature stress-mediated metamorphosis regulation of lepidopteran insect has not been elucidated. In this study, the relationship between the insect developmental process and endogenous hormone level was investigated under high temperature (36 ° C) stress inBombyx mori(B. mori). The results showed that the duration of 5thinstar larvae were shortened by 28 ± 2 h, and the content of 20E was up-regulated significantly after 72 h of high temperature treatment, while the transcription levels of 20E response genesE93, Br-C, USP, E75were up-regulated 1.35, 1.25, 1.28, and 1.27-fold, respectively. The high temperature treatment promoted the phosphorylation level of Akt and the downstream BmCncC/keap1 pathway was activated, the transcription levels of 20E synthesis-related genescyp302a1, cyp306a1, cyp314a1andcyp315a1were up-regulated by 1.12, 1.51, 2.17 and 1.23-fold, respectively. After treatment with double stranded RNA of BmCncC (dsBmCncC) in BmN cells, the transcription levels ofcyp302a1andcyp306a1were significantly decreased, whereas up-regulated by 2.15 and 1.31-fold, respectively, after treatment with CncC activator Curcumin. These results suggested that BmCncC/keap1-mediated P450 genes (cyp302a1, cyp306a1) expression resulted in the changes of endogenous hormone level, which played an important role in the regulation of metamorphosis under high temperature stress. Studies provide novel clues for understanding the CncC/keap1 pathway-mediated metamorphosis regulation mechanism in insects.

Author Summary

Mammalian nuclear transcription factor Nrf2 (NF-E2-related factor 2) plays an important role in the stress response of cells. CncC is a homolog of mammalian Nrf2 in insect, regulating the genes expression of insect antioxidant enzymes and cytochrome P450 detoxification enzyme. Evidence suggests that the CncC/Keap1 pathway also plays an important role in regulating insect development. Here, we investigated the regulatory mechanism between the CncC/Keap1 pathway and metabolism of silkworm hormones in Lepidoptera. We found that high temperature induction accelerated the development of silkworm, the ecdysone content and related metabolic genes in hemolymph were significantly up-regulated, the CncC/Keap1 pathway was activated, and the expression ofBmCncCwas significantly increased, indicating that the Cncc/Keap1 pathway plays an important role in this process. The expression ofcyp302a1andcyp306a1was significantly decreased by RNA interference withBmCncC, which indicated that CncC in silkworm had a regulatory relationship with downstream 20E synthetic gene. In summary, the results indicate that the CncC/Keap1 pathway plays an important role in regulating hormone metabolism in silkworm, providing a basis for further study of the relationship between CncC/Keap1 pathway and development in insects.