Postdoctoral Advisor: Dr. Norbert H. Haunerland, Simon Fraser University

In all animals, the effective utilization and storage of nutrients is essential for reproductive fitness. Energy reserves are most effectively stored as lipids, while amino acid reserves are necessary for the biosynthetic activities of adults and developing offspring. Lipoproteins are the common transport and storage form of these nutrients, and their expression and assembly needs to be coordinated with nutrient availability, reproductive behaviour, and the physiological state of the animal. While past research points to endocrine control and nutritional feedback mechanisms, these regulatory mechanisms are only poorly understood at the molecular level. Building on my physiological expertise in the ecophysiology of lipoproteins in passerine birds, I aimed to study these mechanisms at the level of gene regulation.

Fifth instar Helicoverpa zea larva

The main objective of my research was to identify regulatory elements in the promoter regions of the H. zea VHDL and VTG genes and assess their roles in the stage-specific expression of the VHDL gene in last instar larvae and the VTG gene in adult females. Using GFP reporter gene assays and quantitative real-time PCR, I assessed differential GFP expression under the control of various promoter constructs derived from the VHDL and VTG genes and in response to a variety of hormonal and nutritional conditions, including those associated with either the last larval instar or adult reproductive stages.

I investigated the regulation of two closely-related genes in the corn earworm (Helicoverpa zea) that fulfill analogous roles at different life stages: the gene for the yolk protein precursor, vitellogenin (VTG), and the gene for a larval-specific very-high density lipoprotein (VHDL). Both VTG and VHDL are storage proteins which are synthesized in the fat body, secreted into the hemolymph, and are involved in transporting and storing amino acids and lipids in other tissues where they are subsequently broken down for use in the biosynthesis of structures of a different life stage (larva or pharate adult, respectively) (Sum and Haunerland 2007). Both genes appear to be under the control of reproductive hormones, but the mechanisms are not yet understood. VTG expression occurs only in adult females when juvenile hormone (JH) levels are high, while the VHDL gene is expressed only during the last larval instar when endogenous JH is absent.

Understanding the regulatory mechanisms underlying stage-specific expression of the VHDL and VTG genes will aid in the understanding of the common and dissimilar characteristics of these closely related genes, including the their unusually high expression levels and contrasting endocrine regulation. The relatively simple model system employed here shares many of the physiological characteristics with vertebrates, and may thus provide insights into the regulation of general and reproductive lipoproteins in more complex animal systems.

Cloning the H. zea vitellogenin promoter

Related publications

Kim, J.J.K., Sum, H., Cheema, M.G., Salvante, K.G., Bernales, C.Q., Rickers-Haunerland, J., and Haunerland, N.H. 2010. Juvenile hormone mediated, stage specific expression of large lipid transfer proteins in the corn earworm, Helicoverpa zea (Lepidoptera, Noctuidae). Chemistry and Physics of Lipids 163 Suppl:S56.