Abstract
Honey bees and bumble bees belong to the same family (Apidae) and their workers exhibit a division of labor, but the style of division of labor differs between species. The molecular and neural bases of the species-specific social behaviors of Apidae workers have not been analyzed. Here, we focused on two immediate early genes, hormone receptor 38 (HR38) and early growth response gene-1 (Egr1), and late-upregulated ecdysone receptor (EcR), all of which are upregulated by foraging flight and expressed preferentially in the small-type Kenyon cells of the mushroom bodies (MBs) in the honey bee brain. Gene expression analyses in Bombus ignitus revealed that HR38 and Egr1, but not EcR, exhibited an immediate early response during awakening from CO2 anesthesia. Both premature mRNA for HR38 and mature mRNA for Egr1 were induced during foraging flight, and mRNAs for HR38 and Egr1 were sparsely detected inside the whole MB calyces. In contrast, EcR expression was higher in forager brains than in nurse bees and was expressed preferentially in the small-type Kenyon cells inside the MBs. Our findings suggest that Kenyon cells are active during foraging flight and that the function of late-upregulated EcR in the brain is conserved among these Apidae species.
Highlights
Honey bees and bumble bees belong to the same family (Apidae) and their workers exhibit a division of labor, but the style of division of labor differs between species
We first examined whether BiHR38, BiEgr[1], and BiEcR show an immediate early response
BiEgr[1] was induced earlier (~30 min after the cessation of anesthesia) than BiHR38 (~60 min; Fig. 3a,c), which is consistent with previous studies in moths[34], flies[34], honey bees[31], and mammals[43]
Summary
Honey bees and bumble bees belong to the same family (Apidae) and their workers exhibit a division of labor, but the style of division of labor differs between species. Previous studies used immediate early genes (IEGs), whose expression is rapidly upregulated after neuronal activation, to identify the brain regions related to certain behaviors[26] Findings from these studies using a battery of IEGs, such as kakusei (noncoding RNA identified from A. mellifera)[27], Egr[1] (early growth response gene-1, known as NGFI-A, Krox[24], zif[268], and zenk)[28,29,30,31], and HR38 (hormone receptor 38, the subfamily of nuclear receptor 4A)[23,32,33,34], suggested a possible role of the sKCs and some mKCs in the MBs in sensory processing during the foraging flight in honey bees[12]. These results suggest that neural activity in the forager brain and the function of ecdysone signaling in the sKCs are conserved among these two species
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