Nuclear receptors of the honey bee: annotation and expression in the adult brain

The Drosophila genome encodes 18 canonical nuclear receptors. All of the Drosophila nuclear receptors are here shown to be present in the genome of the honey bee (Apis mellifera). Given that the time since divergence of the Drosophila and Apis lineages is measured in hundreds of millions of years, the identification of matched orthologous nuclear receptors in the two genomes reveals the fundamental set of nuclear receptors required to ‘make’ an endopterygote insect. The single novelty is the presence in the A. mellifera genome of a third insect gene similar to vertebrate photoreceptor-specific nuclear receptor (PNR). Phylogenetic analysis indicates that this novel gene, which we have named AmPNR-like, is a new member of the NR2 subfamily not found in the Drosophila or human genomes. This gene is expressed in the developing compound eye of the honey bee. Like their vertebrate counterparts, arthropod nuclear receptors play key roles in embryonic and postembryonic development. Studies in Drosophila have focused primarily on the role of these transcription factors in embryogenesis and metamorphosis. Examination of an expressed sequence tag library developed from the adult bee brain and analysis of transcript expression in brain using in situ hybridization and quantitative RT-PCR revealed that several members of the nuclear receptor family (AmSVP, AmUSP, AmERR, AmHr46, AmFtz-F1, and AmHnf-4) are expressed in the brain of the adult bee. Further analysis of the expression of AmUSP and AmSVP in the mushroom bodies, the major insect brain centre for learning and memory, revealed changes in transcript abundance and, in the case of AmUSP, changes in transcript localization, during the development of foraging behaviour in the adult. Study of the honey bee therefore provides a model for understanding nuclear receptor function in the adult brain

Visual Associative Learning in Restrained Honey Bees with Intact Antennae

A restrained honey bee can be trained to extend its proboscis in response to the pairing of an odor with a sucrose reward, a form of olfactory associative learning referred to as the proboscis extension response (PER). Although the ability of flying honey bees to respond to visual cues is well-established, associative visual learning in restrained honey bees has been challenging to demonstrate. Those few groups that have documented vision-based PER have reported that removing the antennae prior to training is a prerequisite for learning. Here we report, for a simple visual learning task, the first successful performance by restrained honey bees with intact antennae. Honey bee foragers were trained on a differential visual association task by pairing the presentation of a blue light with a sucrose reward and leaving the presentation of a green light unrewarded. A negative correlation was found between age of foragers and their performance in the visual PER task. Using the adaptations to the traditional PER task outlined here, future studies can exploit pharmacological and physiological techniques to explore the neural circuit basis of visual learning in the honey bee

A new member of the GM130 golgin subfamily is expressed in the optic lobe anlagen of the metamorphosing brain of Manduca sexta

During metamorphosis of the insect brain, the optic lobe anlagen generate the proliferation centers for the visual cortices. We show here that, in the moth Manduca sexta, an 80 kDa Golgi complex protein (Ms-golgin80) is abundantly expressed in the cytoplasm of neuroblasts and ganglion mother cells in the optic lobe anlagen and proliferation centers. The predicted amino acid sequence for Ms-golgin80 is similar to that of several members of the GM130 subfamily of Golgi-associated proteins, including rat GM130 and human golgin-95. Homologs of Ms-golgin80 from Drosophila melanogaster, Caenorhabditis elegans, and Brugia malayi were identified through homology sequence search. Sequence similarities are present in three regions: the N-terminus, an internal domain of 89 amino acids, and another domain of 89 amino acids near the C-terminus. Structural similarities further suggest that these molecules play the same cellular role as GM130. GM130 is involved in the docking and fusion of coatomer (COP I) coated vesicles to the Golgi membranes; it also regulates the fragmentation and subsequent reassembly of the Golgi complex during mitosis. Abundant expression of Ms-golgin80 in neuroblasts and ganglion mother cells and its reduced expression in the neuronal progeny of these cells suggest that this protein may be involved in the maintenance of the proliferative state.published or submitted for publicationis peer reviewe

Stimulation of muscarinic receptors mimics experience-dependent plasticity in the honey bee brain

Honey bees begin life working in the hive. At ≈3 weeks of age, they shift to visiting flowers to forage for pollen and nectar. Foraging is a complex task associated with enlargement of the mushroom bodies, a brain region important in insects for certain forms of learning and memory. We report here that foraging bees had a larger volume of mushroom body neuropil than did age-matched bees confined to the hive. This result indicates that direct experience of the world outside the hive causes mushroom body neuropil growth in bees. We also show that oral treatment of caged bees with pilocarpine, a muscarinic agonist, induced an increase in the volume of the neuropil similar to that seen after a week of foraging experience. Effects of pilocarpine were blocked by scopolamine, a muscarinic antagonist. Our results suggest that signaling in cholinergic pathways couples experience to structural brain plasticity

Age of forager honey bees and visual conditioning performance were negatively correlated.

<p>A. A negative relationship was found between age of foragers tested in this study and the number of cumulative responses on the rewarded trials prior to sucrose presentation (Pearson’s correlation, r = −0.684, n = 9, <i>p</i> = 0.042). B. A positive relationship was found between age and the minimum number of trials required to reach the threshold of learning (3 cumulative responses; Pearson’s correlation, r = 0.719, n = 9, <i>p</i> = 0.029).</p

Insect nuclear receptors

The nuclear receptors (NRs) of metazoans are an ancient family of transcription factors defined by conserved DNA- and ligand-binding domains (DBDs and LBDs, respectively). The Drosophila melanogaster genome project revealed 18 canonical NRs (with DBDs and LBDs both present) and 3 receptors with the DBD only. Annotation of subsequently sequenced insect genomes revealed only minor deviations from this pattern. A renewed focus on functional analysis of the isoforms of insect NRs is therefore required to understand the diverse roles of these transcription factors in embryogenesis, metamorphosis, reproduction, and homeostasis. One insect NR, ecdysone receptor (EcR), functions as a receptor for the ecdysteroid molting hormones of insects. Researchers have developed nonsteroidal ecdysteroid agonists for EcR that disrupt molting and can be used as safe pesticides. An exciting new technology allows EcR to be used in chimeric, ligand-inducible gene-switch systems with applications in pest management and medicine

Harnessed, antenna-intact forager honey bees can learn to respond differentially to color stimuli.

<p>A, B. All forager honey bees completing visual training. C, D. Only those foragers that responded more than 3 cumulative times to light presentation prior the US (learners). A, C. The percentage of responses to light presentation on each trial. B, D. The average number of cumulative responses. Comparison of responses on trial 10 (A, C) used Chi-square test. Comparison of total cumulative responses (B, D) used Mann-Whitney U test. *<i>p</i><0.005, **<i>p</i><0.001, ***p<0.0001.</p

Forager honey bees conditioned with a wet toothpick as the US

<p>^–<b>show reduced learning.</b> The percentage of honey bees in each group that reached the learning threshold is depicted here. The Fisher exact probability test was used to compare the number of responders in each category (dry: 9/15; water: 4/19; null: 6/9). Letters indicate significant differences (<i>α</i><0.05). Groups designated with the same letter did not differ.</p

Description of the experimental paradigm.

<p>A. Worker honey bees were restrained in plastic drinking straws using a yoke made of insect pins placed on either side on the neck. Honey bees were supported from below using a rolled paper tissue. A small window was cut in the straw to allow full extension of the proboscis. B. Restrained honey bees were placed in front of individual light presentation screens. Each screen could be illuminated with a blue or green led and had a red LED mounted on top to indicate US presentation to the experimenter. C. A series of projection screens allowed simultaneous conditioning of up to ten honey bees. D. Both the rewarded and unrewarded trials used the same timing of CS/US presentation. Following a 3 sec countdown (not depicted), the CS presentation lasted 5 sec during the final 3 sec of which the US was presented. Proboscis extensions (responses) were recorded to the CS before and during the US presentation.</p