Honey bee foraging induces upregulation of early growth response protein 1, hormone receptor 38 and candidate downstream genes of the ecdysteroid signalling pathway

Abstract

In honey bees, continuous foraging at an artificial feeder induced a sustained upregulation of the immediate early genes early growth response protein 1 (Egr-1) and hormone receptor 38 (Hr38). This gene expression response was accompanied by an upregulation of several Egr-1 candidate downstream genes: ecdysone receptor (EcR), dopamine/ecdysteroid receptor (DopEcR), dopamine decarboxylase and dopamine receptor 2. Hr38, EcR and DopEcR are components of the ecdysteroid signalling pathway, which is highly probably involved in learning and memory processes in honey bees and other insects. Time-trained foragers still showed an upregulation of Egr-1 when the feeder was presented at an earlier time of the day, suggesting that the genomic response is more dependent on the food reward than training time. However, presentation of the feeder at the training time without food was still capable of inducing a transient increase in Egr-1 expression. Thus, learnt feeder cues, or even training time, probably affect Egr-1 expression. In contrast, whole brain Egr-1 expression changes did not differ between dancing and nondancing foragers. On the basis of our results we propose that food reward induced continuous foraging ultimately elicits a genomic response involving Egr-1 and Hr38 and their downstream genes. Furthermore this genomic response is highly probably involved in foragingrelated learning and memory responses.

Immediate early gene kakusei plays a role in the daily foraging and learning of honey bees

“…This study extends our recent report [12] on the search for immediate early genes (IEGs) that could be used as search tool towards finding the molecular and cellular mechanisms underlying social behavior using foraging of honey bees as model system. As the foraging of bees consists of systematically well organized social behaviors that include learning, memory, social interaction and communication etc; honey bee foraging has been extensively studied in various research objectives in connection to social behavior.…”

“…The present study represents further investigation of immediate early genes (IEG) that could play a role during the daily foraging of honey bees, and is an expansion of our previous report by Singh et al [12]. We selected two potential IEGs kakusei and c-jun, and four other orthologous genes that have been reported to be involved in cognitive process in vertebrates: extracellular signal-related kinase (rk7), glutamate receptor (GluR), 5-hydroxy tryptamine (serotonin) receptor 2 alpha (5-HT2α) and dopamine receptor 1 (Dop1).…”

“…For the gene expression profiling, nectar foragers were collected and the gene expression analysis was carried out with those samples. The procedures were previously described [12].…”

“…In addition, depending on the type of the stimuli, the IEG-encoded proteins can be individually regulated in different parts of the brain [8,11], indicating that the same or different IEGs, when expressed in different parts of the brain, regulate different functions. In our recent work, we have demonstrated involvement of two IEGs i.e., early growth response 1 (egr-1), nuclear hormone receptor 38 (hr38) and their corresponding partner genes such as ecdysone receptor (ecr), dopamine/ecdysteroid receptor (dopecr), dopamine decarboxylase (ddc) and dopamine receptor 2 (dopr2) during the daily foraging of bees [12]. Other papers reported on the involvement of egr-1 in the transition from nursing to foraging bees [13] and the role of hr38 in caste and labor division [14], while the other genes were shown to be act as egr-1 downstream genes involved in ecdysteroid and dopamine signaling with a role in the processing of courtship memory [15] in Drosophila and in olfactory learning and memory [16] in honey bees, respectively.…”

The insect HR38 nuclear receptor, a member of the NR4A subfamily, is a synchronizer of reproductive activity in a moth

“…Furthermore, we cannot exclude that AiHR38 could act in other brain regions than ALs. This possibility is supported by several studies showing that the expression of HR38 is not restricted to the AL but can also be found within higher order olfactory centres including the protocerebrum and the mushroom bodies and that the brain HR38 expression was induced by the foraging behaviour in A. mellifera [30,31] and in response to sex pheromone in B. mori and D. melanogaster males [29].…”