Abstract
Developing oocytes accumulate plentiful yolk protein during oogenesis through receptor-mediated endocytosis. The vitellogenin receptor (VgR), belonging to the low-density lipoprotein receptor (LDLR) family, regulates the absorption of yolk protein. In this work, the full-length vitellogenin receptor (HaVgR) in the cotton bollworm Helicoverpa armigera was identified, encoding a 1817 residue protein. Sequence alignment revealed that the sequence of HaVgR contained all of the conservative structural motifs of LDLR family members, and phylogenetic analysis indicated that HaVgR had a high identity among Lepidoptera and was distinct from that of other insects. Consistent with other insects, HaVgR was specifically expressed in ovarian tissue. The developmental expression pattern showed that HaVgR was first transcribed in the newly metamorphosed female adults, reached a peak in 2-day-old adults and then declined. Western blot analysis also revealed an ovarian-specific and developing expression pattern, which was consistent with the HaVgR mRNA transcription. Moreover, RNAi-mediated HaVgR knockdown strongly reduced the VgR expression in both the mRNA and protein levels, which inhibited the yolk protein deposition in the ovaries, led to the dramatic accumulation of vitellogenin and the up-regulation of HaVg expression in hemolymph, and eventually resulted in a declined fecundity. Together, all of these findings demonstrate that HaVgR is a specific receptor in uptake and transportation of yolk protein for the maturation of oocytes and that it plays a critical role in female reproduction.
Highlights
In insects, developing oocytes accumulate large amounts of vitellogenin (Vg) to meet the nutrient requirement for egg development
Analyses of the HaVgR protein sequence indicated that, similar to other insect vitellogenin receptor (VgR), it contained all of the features that are typical of the low-density lipoprotein receptor (LDLR) family
HaVgR exhibited two ligand-binding domains (LBDs) with four class A (LDLRA) cysteine-rich repeats in the first domain (LBD1) and seven repeats in the second domain (LBD2)
Summary
In insects, developing oocytes accumulate large amounts of vitellogenin (Vg) to meet the nutrient requirement for egg development. As the major yolk protein, Vg is primarily synthesized in the fat body for release into the circulatory system and is subsequently taken up by the competent oocytes [1]. This uptake is achieved by the vitellogenin receptor (VgR) which is located within clathrin-coated pits on the surface of growing competent oocytes [1,2,3]. A yolk protein receptor functioning as the VgR has been well documented in the fruit fly [17] These studies demonstrated that VgR mediated the Vg uptake during insect reproduction, VgR could serve as a potential target for pest control [1, 2]. Previous studies of VgR were mainly focused on the limited species of hygiene pests and beneficial insects, and few studies were focused on agricultural pests, the notorious Lepidoptera moths
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