Characterization of a Vitellogenin Receptor in the Bumblebee, Bombus lantschouensis (Hymenoptera, Apidae).

The vitellogenin receptor (VgR) belongs to the low-density lipoprotein receptor (LDLR) family, responsible for mediating the endocytosis of vitellogenin (Vg) into the ovaries to promote ovarian growth and oviposition. Here, we cloned and measured VgR gene expression characteristics in the bumblebee Bombus lantschouensis. RNA interference was used to validate VgR function. The results showed that the full length of the BLVgR cDNA was 5519 bp, which included a 5280 bp open reading frame encoding 1759 amino acids (AAs). Sequence alignment revealed that the protein contained 12 LDLa, 5 EGF, 2 EGF-CA and 10 LY domains. Phylogenetic analysis showed that BLVgR and the VgR of Bombus terrestris clustered together and the tree of bumblebees (Bombus) appeared as one clade next to honeybees (Apis). Transcript expression analysis showed that BLVgR was expressed in all tested tissues and showed the highest abundance in the ovaries. BLVgR expression was present in all developmental stages. However, the expression level in larvae was extremely low. In addition, the expression of BLVgR was significantly upregulated after egg laying in both workers and queens. In new emerging workers injected with 5 µg of VgR dsRNA, the expression level of BLVgR was 4-fold lower than that in the GFP dsRNA-injected group after 72 h. Furthermore, BLVgR silencing significantly reduced the number of eggs laid (3.67 ± 1.96 eggs) and delayed the first egg-laying time (16.31 ± 2.07 days) in worker microcolonies when compared to dsGFP (37.31 ± 4.09 eggs, 8.15 ± 0.22 days) and DEPC-treated water injected controls (16.42 ± 2.24 eggs, 10.00 ± 0.37 days). In conclusion, the BLVgR gene and its reproductive function were explored in the bumblebee B. lantschouensis. This gene plays an important role in egg laying time and egg number.