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Molecular Analysis of Juvenile Hormone Action in Heliothis virescens
S.R. Palli
Department of Entomology
Project Description
Development Tribolium castaneum as a model system to study JH action: The insect midgut epithelium is remodeled during larval-pupal metamorphosis when larval polyploid cells (LPCs) are replaced by the daughters of intestinal stem cells (ISCs). We characterized the proliferation of ISCs during midgut remodeling in the red flour beetle, Tribolium castaneum. Midgut remodeling is initiated at 96 hr after ecdysis into the final instar larval stage. Immunocytochemistry with bromodeoxyuridine and phospho-histone H3 antibodies showed that the ISCs are the progenitors of the pupal/adult midgut epithelium and they undergo proliferation and differentiation to form new midgut epithelium. In vitro midgut culture experiments revealed that 20-hydroxyecdysone (20E) in the absence of juvenile hormone induces proliferation of ISCs. RNA interference (RNAi) mediated silencing of ecdysone receptors (EcRA and EcRB) and ultraspiracle (USP) identified EcRA and USP but not EcRB as the proteins involved in 20E regulation of ISCs proliferation. These data show that the proliferation of ISCs is under both developmental and endocrine regulation.
Impact
The long-term goals of this research are to understand the molecular basis of juvenile hormone action and use this information to (a) understand the mode of action of existing hormone analogs, (b) develop target-site based screening assays to discover new, more potent, species-specific, environmentally benign hormone analogs, (c) interfere with insect development by over or under expressing critical genes involved in JH action through recombinant microorganisms, transgenic insects or transgenic plants and (d) develop gene switches for controlling the expression of transgenes in plants, animals and human beings.
Publications
Parthasarathy, R. and Palli, S.R. (2007) Developmental and hormonal regulation of midgut remodeling in a lepidopteran insect, Heliothis virescens. Mechanisms of Development 124, 23-34.
Parthasarathy, R. and Palli, S. R. (2008) Proliferation and differentiation of intestinal stem cells during metamorphosis of the red flour beetle, Tribolium castaneum Dev.Dyn. (In press).