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Molecular Analysis of Juvenile Hormone Action in the Red Flour Beetle, Tribolium cataneum
Department of Entomology
There has been a continuous demand for the development of insect control methods that are target-specific. Juvenile hormone (JH) and ecdysteroids (20-hydroxyecdysone, 20E is the most active form) are the major hormones that regulate development and reproduction in insects. Since these hormones are not present in vertebrates, they represent attractive targets for the development of insect control methods. Hindering this effort is the lack of understanding of the molecular basis of JH action. We propose to study mechanism of JH action in regulation of vitellogenin gene expression in the fat body.
Completion of whole genome sequencing, availability of microarrays, functioning of systemic RNA interference (RNAi) and excellent response to JH and its analogs make T. castaneum an excellent model system for studies on JH action. Microarray, RNAi, qRT-PCR, electrophoretic mobility shift assays and ligand-binding assays will be employed to identify and characterize receptors, transcription factors and protein modifiers involved in JH regulation of vitellogenin gene expression JH analogs are being used for pest management, but some pests are already developing resistance to these analogs.
The results from these studies will aid in understanding the mode of action of JH analogs, thus facilitating their judicious use. The genes identified will be useful to develop screening assays to identify new insect disease vector control agents. The receptors identified can also be used in agriculture by developing gene switches for various applications such as regulated expression of transgenes in crop plants.
2011 Project Description
Female reproduction includes maturation of oocytes and the synthesis of yolk proteins (vitellogenin, Vg) in the fat body and their deposition into the oocytes. Our recent studies showed that juvenile hormone (JH) regulates Vg synthesis and 20-hydroxyecdysone (20E) regulates oocyte maturation in the red flour beetle (Tribolium castaneum). We studied the role of nutritional signaling on vitellogenesis and oogenesis.
Comparison of gene expression between fed and starved beetles by microarray analysis showed the up-regulation of genes involved in energy homeostasis and down-regulation of genes involved in egg production in the starved beetles. The RNA interference (RNAi) aided knock-down in the expression of genes involved in insulin and TOR signaling pathways showed that both these signaling pathways play key roles in Vg synthesis and oocyte maturation.
Starvation of female beetles resulted in a block in Vg synthesis but not in the progression of primary oocyte development to the resting stage. Feeding after starvation induced Vg synthesis and the progression of primary oocytes from the resting stage to the mature stage. However, in the beetles where JH or 20E synthesis or action was blocked by RNAi, both Vg synthesis and oocyte maturation were affected suggesting that both these hormones (JH and 20E) and nutritional signaling and their cross-talk regulate vitellogenesis and oogenesis.
The findings reported here will help in designing better insect control methods.
Bai H, Zhu F, Shah K, Palli S.R. (2011) Large-scale RNAi screen of G protein-coupled receptors involved in larval growth, molting and metamorphosis in the red flour beetle. BMC Genomics.12:388.
Parthasarathy, R. & Palli, S. R. (2011) Molecular analysis of nutritional and hormonal regulation of female reproduction in the red flour beetle, Tribolium castaneum, Insect Biochem Mol Biol. 41, 294-305.
Zhang, Z., Xu, J., Sheng, Z., Sui, Y. & Palli, S. R. (2011) Steroid receptor co-activator is required for juvenile hormone signal transduction through a bHLH-PAS transcription factor, methoprene tolerant, J Biol Chem. 286, 8437-47.
Zhu, F., Xu, J., Palli, R., Ferguson, J. & Palli, S. R. (2011) Ingested RNA interference for managing the populations of the Colorado potato beetle, Leptinotarsa decemlineata, Pest Manag Sci. 67, 175-82.107.