Abstract
During reproduction, vitellogenin (Vg), as an egg yolk precursor, is critical in sexually mature females of oviparous species including some insects. The transcription of Vg is usually mediated by hormones such as juvenile hormone (JH), ecdysteroids and some neuropeptides. In this study, the structure of the Vg gene from the bumblebee Bombus lantschouensis, (BlVg) was determined by sequencing and assembly. BlVg was found to be expressed at higher levels in reproductive queens than in virgins by quantitative real-time PCR analysis. Tissue-specific expression analysis showed that BlVg was expressed at the highest levels in the fat bodies of both virgin and reproductive queens. Prediction of the BlVg promoter revealed the presence of ecdysteroid-responsive cis-regulatory elements (CREs) containing one Broad-Complex zinc-finger isoform 3 (BR-C Z3), and one ecdysone-induced protein 74A (E74A). In addition, luciferase reporter expression, driven by the 5' -regulatory region of the BlVg gene, from −1517 bp to +895 bp downstream of the start codon, was induced by treatment with 20-hydroxyecdysone (20-E). Moreover, the luciferase activity of the BlVg promoter was elevated by only BlBrC-Z3 when Sf9 cells were cotransfected with four BlBrC isoforms respectively. BlVg promoter-mediated luciferase activation was significantly reduced when the putative BrC-Z3 CRE in the promoter was mutated. In summary, this report describes the first study of vitellogenin gene regulation at the transcriptional level in bumblebees and demonstrates that the ecdysone-induced transcription of the BlVg gene is mediated by the binding of BlBrC-Z3 to the BrC-Z3 CRE in the BlVg promoter in bumblebees.
Highlights
Insect vitellogenin (Vg), a large phosphoglycolipoprotein, is the major yolk protein precursor synthesized mainly by the fat body in sexually mature females [1, 2]
We describe the gene structure, expression pattern and transcriptional regulation of the Vg gene from the bumblebee B. lantschouensis (BlVg)
There was little amino acid difference between the protein from B. lantschouensis and those from other Bombus species (e.g. B. ignitus, B. hypocrita, and B. terrestris), which was consistent with the phylogenetic analysis (Fig 1B)
Summary
Insect vitellogenin (Vg), a large phosphoglycolipoprotein, is the major yolk protein precursor synthesized mainly by the fat body in sexually mature females [1, 2]. Because of its association with fecundity and reproduction, Vg has been extensively studied in many insects, including Hymenoptera. Vitellogenin transcription in bumblebee is mediated by Broad-Complex Z3 known to involve in the development of honeybees, such as social behavior/organization [3,4,5,6], aging [7,8,9,10], and protection from various stress [11, 12]. Vg plays a crucial role in insect reproduction. It is necessary to decipher the transcriptional profiles and regulation mechanism of the Vg gene in Bombus lantschouensis
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