Nutrient sensitive insulin-like peptides (ILPs) have profound effects on invertebrate metabolism, nutrient storage, fertility and aging. Many insects transcribe ILPs in specialized neurosecretory cells at changing levels correlated with life history. However, the major site of insect metabolism and nutrient storage is not the brain, but rather the fat body, where functions of ILP expression are rarely studied and poorly understood. Fat body is analogous to mammalian liver and adipose tissue, with nutrient stores that often correlate with behavior. We used the honey bee (Apis mellifera), an insect with complex behavior, to test whether ILP genes in fat body respond to experimentally induced changes of behavioral physiology. Honey bee fat body influences endocrine state and behavior by secreting the yolk protein precursor vitellogenin (Vg), which suppresses lipophilic juvenile hormone and social foraging behavior. In a two-factorial experiment, we used RNA interference (RNAi)-mediated vg gene knockdown and amino acid nutrient enrichment of hemolymph (blood) to perturb this regulatory module. We document factor-specific changes in fat body ilp1 and ilp2 mRNA, the bee's ILP-encoding genes, and confirm that our protocol affects social behavior. We show that ilp1 and ilp2 are regulated independently and differently and diverge in their specific expression-localization between fat body oenocyte and trophocyte cells. Insect ilp functions may be better understood by broadening research to account for expression in fat body and not only brain.
↵* These authors contributed equally to this work
Supplementary material available online at http://jeb.biologists.org/cgi/content/full/214/9/1488/DC1
Support to G.V.A. was provided by the Norwegian Research Council (180504, 185306, 191699), the PEW Foundation and the National Institute of Aging (NIA P01 AG22500). K.H. was supported by CNPq (305378/2007-4). K.E.I. was supported by a National Science Foundation Doctoral Dissertation Improvement Grant (0910330) and an Arizona State University–Smithsonian Tropical Research Institute post-doctoral award. Deposited in PMC for release after 12 months.
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