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RNA Interference-Mediated Suppression of Ecdysone Signaling Inhibits Choriogenesis in Two Coleoptera Species
Xiao-Qing Zhang1, Lin Jin1, Wen-Chao Guo2,3
1Education Ministry Key Laboratory of Integrated Management of Crop Diseases and Pests, State & Local Joint Engineering Research Center of Green Pesticide Invention and Application, Department of Entomology, College of Plant Protection, Nanjing Agricultural University, Nanjing 210095, China.
Abstract:
During choriogenesis in insects, chorion (eggshell) is formed by surrounding follicular epithelial cells in ovarioles. However, the regulatory endocrine factor(s) activating choriogenesis and the effect of chemical components on eggshell deserve further exploration. In two representative coleopterans, a coccinellid Henosepilachna vigintioctopunctata and a chrysomelid Leptinotarsa decemlineata, genes encoding the 20-hydroxyecdysone (20E) receptor heterodimer, ecdysone receptor (EcR) and ultraspiracle (USP), and two chitin biosynthesis enzymes UDP-N-acetylglucosamine pyrophosphorylase (UAP) and chitin synthase (ChS1), were highly expressed in ovaries of the young females. RNA interference (RNAi)-aided knockdown of either HvEcR or Hvusp in H. vigintioctopunctata inhibited oviposition, suppressed the expression of HvChS1, and lessened the positive signal of Calcofluor staining on the chorions, which suggests the reduction of a chitin-like substance (CLS) deposited on eggshells. Similarly, RNAi of LdEcR or Ldusp in L. decemlineata constrained oviposition, decreased the expression of LdUAP1 and LdChS1, and reduced CLS contents in the resultant ovaries. Knockdown of LdUAP1 or LdChS1 caused similar defective phenotypes, i.e., reduced oviposition and CLS contents in the L. decemlineata ovaries. These results, for the first time, indicate that 20E signaling activates choriogenesis in two coleopteran species. Moreover, our findings suggest the deposition of a CLS on the chorions.
Insights
The study reveals that 20-hydroxyecdysone (20E) signaling activates insect eggshell formation (choriogenesis). This process involves chitin biosynthesis and results in a chitin-like substance (CLS) deposited on the eggshells of two beetle species.
Area of Science:
- Insect reproductive biology
- Endocrinology
- Biochemistry
Background:
- Choriogenesis, the formation of the insect eggshell (chorion), is crucial for reproduction.
- The endocrine factors regulating choriogenesis and the chemical composition of eggshells remain incompletely understood.
- 20-hydroxyecdysone (20E) is a key insect hormone, but its specific role in choriogenesis requires further investigation.
Purpose of the Study:
- To investigate the role of 20-hydroxyecdysone (20E) signaling in activating choriogenesis in coleopteran insects.
- To explore the involvement of chitin biosynthesis pathway genes in eggshell formation.
- To determine the presence and significance of chitin-like substances (CLS) in the insect eggshell.
Main Methods:
- Gene expression analysis of ecdysone receptor (EcR), ultraspiracle (USP), UDP-N-acetylglucosamine pyrophosphorylase (UAP), and chitin synthase (ChS1) in ovaries of two coleopteran species.
- RNA interference (RNAi) to knock down the expression of EcR, USP, UAP, and ChS1 genes.
- Assessment of oviposition rates, gene expression levels, and chitin-like substance (CLS) content in chorions following gene knockdown.
Main Results:
- Genes for the 20E receptor heterodimer (EcR/USP) and chitin synthesis enzymes (UAP, ChS1) were highly expressed in young female ovaries.
- RNAi-mediated knockdown of EcR, USP, UAP, or ChS1 genes in *Henosepilachna vigintioctopunctata* and *Leptinotarsa decemlineata* led to inhibited oviposition and reduced expression of chitin synthesis genes.
- Knockdown treatments also resulted in decreased chitin-like substance (CLS) deposition on the eggshells, indicated by reduced Calcofluor staining.
Conclusions:
- 20-hydroxyecdysone (20E) signaling is a critical activator of choriogenesis in the studied coleopteran species.
- The study provides the first evidence for 20E's role in activating choriogenesis in these insects.
- A chitin-like substance (CLS) is deposited on the chorions, and its formation is regulated by 20E signaling and chitin biosynthesis pathways.
