Gustatory Perception and Fat Body Energy Metabolism Are Jointly Affected by Vitellogenin and Juvenile Hormone in Honey Bees

Amdam GV (2012) Gustatory Perception and Fat Body Energy Metabolism Are Jointly Affected by Vitellogenin and Juvenile Hormone in Honey Bees. PLoS Genet 8(6): e1002779. doi:10.1371/journal.pgen.1002779 Gustatory Perception and Fat Body Energy Metabolism Are Jointly Affected by Vitellogenin and Juvenile Hormone in Honey Bees Ying Wang 0 Colin S. Brent 0 Erin Fennern 0 Gro V. Amdam 0 Eric Rulifson, University of California San Francisco, United States of America 0 1 School of Life Sciences, Arizona State University , Tempe , Arizona, United States of America, 2 U.S. Department of Agriculture, Arid-Land Agricultural Research Center, Maricopa, Arizona, United States of America, 3 School of Medicine, Oregon Health and Science University , Portland, Oregon , United States of America, 4 Department of Chemistry , Biotechnology, and Food Science , University of Life Sciences , Aas , Norway Honey bees (Apis mellifera) provide a system for studying social and food-related behavior. A caste of workers performs agerelated tasks: young bees (nurses) usually feed the brood and other adult bees inside the nest, while older bees (foragers) forage outside for pollen, a protein/lipid source, or nectar, a carbohydrate source. The workers' transition from nursing to foraging and their foraging preferences correlate with differences in gustatory perception, metabolic gene expression, and endocrine physiology including the endocrine factors vitellogenin (Vg) and juvenile hormone (JH). However, the understanding of connections among social behavior, energy metabolism, and endocrine factors is incomplete. We used RNA interference (RNAi) to perturb the gene network of Vg and JH to learn more about these connections through effects on gustation, gene transcripts, and physiology. The RNAi perturbation was achieved by single and double knockdown of the genes ultraspiracle (usp) and vg, which encode a putative JH receptor and Vg, respectively. The double knockdown enhanced gustatory perception and elevated hemolymph glucose, trehalose, and JH. We also observed transcriptional responses in insulin like peptide 1 (ilp1), the adipokinetic hormone receptor (AKHR), and cGMP-dependent protein kinase (PKG, or ''foraging gene'' Amfor). Our study demonstrates that the Vg-JH regulatory module controls changes in carbohydrate metabolism, but not lipid metabolism, when worker bees shift from nursing to foraging. The module is also placed upstream of ilp1, AKHR, and PKG for the first time. As insulin, adipokinetic hormone (AKH), and PKG pathways influence metabolism and gustation in many animals, we propose that honey bees have conserved pathways in carbohydrate metabolism and conserved connections between energy metabolism and gustatory perception. Thus, perhaps the bee can make general contributions to the understanding of food-related behavior and metabolic disorders. - Funding: This research was supported by the Research Council of Norway (180504, 185306, 191699), the PEW Charitable Trust, and the National Institute on Aging (NIA P01 AG22500). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. Honey bees (Apis mellifera), with their complex social structure, remarkably plastic physiology and well-studied food-related activities, provide a model for connections between behavior and metabolism. Honey bee workers are essentially sterile female helpers that perform different tasks based on their age. In the first 23 weeks of adult life, workers called nurses care for the brood and other nestmates, construct wax combs and clean the nest. In roughly their 4th week of life, workers go through a behavioral transition and begin foraging outside the nest [1]. As foragers, workers can bias food-collection toward proteins (pollen) or carbohydrates (nectar). The transition to foraging behavior is associated with changes in gustatory perception [2], food consumption, hormone levels [35] and expression of genes associated with nutrient sensitivity and metabolism in workers [6 8]. Therefore, studies of honey bee behavioral physiology and genetics may reveal information of general interest in food-related behavior. Gustatory perception is a predictor of honey bee behaviors such as how quickly a worker transitions from nursing to foraging (i.e., her age at foraging onset) and her foraging bias toward nectar vs. pollen (sources of carbohydrate vs. protein/lipid) [9,10]. A workers gustatory perception, or responsiveness, can be quantified by a standard method that involves monitoring her reflex response to an ascending series of sucrose concentrations [11]. Workers that respond to low sucrose concentrations have high gustatory responsiveness, and they forage at younger ages and collect more pollen and less nectar than bees with low gustatory responsiveness [9]. Gustatory sensitivity can also be an indicator of the bees energy status: a worker bee with higher gustatory responsiveness is hungrier [12], and consumes more food (B. Rascon, G.V. Amdam, unpublished data) and dies faster under starvation conditions (M. Speth, G.V. Amdam, unpublished data) compared to a worker with lower gustatory responsiveness. The social behaviors of honey bees are associated with complex energetic physiologies, suggesting that food consumption and foodrelated behavior are linked to energy homeostasis. Nurse bees, Communication between internal energetic state and taste perception helps animals control food uptake and maintain normal life functions. Honey bees provide an animal model for studies of food-related behavior, such as the role of taste sensitivity in choice-making between carbohydrate- and protein-rich foods (nectar versus pollen for honey bees). A young bees taste sensitivity to sugar predicts when she begins foraging later in life and influences her choice of foods. Vitellogenin (Vg), a protein produced in the bees fat cells, and juvenile hormone (JH) influence honey bee taste perception and food-related behavior. Vg and JH are connected by a feedback loop, and we perturbed this VgJH circuit using a double gene knockdown approach. In response, bees became more sensitive to sugar, had higher sugar levels in the blood, and died faster during starvation, while lipid levels remained constant. We identified that insulin like peptide 1 (ilp1), the adipokinetic hormone receptor (AKHR), and PKG (the foraging gene) were altered in the bees fat cells after the perturbation. Our study demonstrates a new role for the VgJH circuit in honey bee carbohydrate metabolism, and it places VgJH upstream of the three metabolic genes that have conserved roles in food-related behaviors and energy metabolism in many animals. which feed on pollen and produce highly proteinaceous food secretions, have more abdominally stored proteins [13,14] and lipids than foragers [15]. Experimental depletion of th (...truncated)