Endocrine modulation of a pheromone-responsive gene in the honey bee brain

Pheromones cause dramatic changes in behavior and physiology, and are critical for honey bee colony organization. Queen mandibular pheromone (QMP) regulates multiple behaviors in worker bees (Slessor et al. in J Chem Ecol 31(11):2731-2745, 2005). We also identified genes whose brain expression levels were altered by exposure to QMP (Grozinger et al. in Proc Natl Acad Sci USA 100(Suppl 2):14519-14525, 2003). Krüppel-homolog 1 (Kr-h1) RNA levels were significantly downregulated by QMP, and were higher in foragers than in nurses (Whitfield et al. in Science 302(5643):296-299, 2003). Here we report on results of behavioral and pharmacological experiments that characterize factors regulating expression of Kr-h1. Foragers have higher brain levels of Kr-h1 than in-hive bees, regardless of age and pheromone exposure. Furthermore, forager Kr-h1 levels were not affected by QMP. Since the onset of foraging is caused, in part, by increasing juvenile hormone blood titers and brain octopamine levels, we investigated the effects of octopamine and methoprene (a juvenile hormone analog) on Kr-h1 expression. Methoprene produced a marginal (not significant) increase in Kr-h1 expression, but Kr-h1 brain levels in methoprene-treated bees were no longer downregulated by QMP. Octopamine did not modulate Kr-h1 expression. Our results demonstrate that the gene expression response to QMP is not hard-wired in the brain but is instead dependent on worker behavioral state.