Regulatory region of the vitellogenin receptor gene sufficient for high-level, germ line cell-specific ovarian expression in transgenic Aedes aegypti mosquitoes.

Vitellogenin receptor (VgR) is responsible for the receptor-mediated endocytosis of vitellogenin (Vg) in the egg formation of an oviparous animal, including insects. Little is known about regulation of VgR gene expression. We analyzed the upstream region of the VgR gene from Aedes aegypti (AaVgR) to identify regulatory elements responsible for its expression in germ cell-specific ovarian expression. Experiments with genetic transformation using the transgene containing the 1.5-Kb upstream portion of the AaVgR gene fused with DsRed and the piggyBac vector showed that this regulatory region is sufficient for correct female and ovary-specific expression of the transgene. This 1.5-Kb upstream region contained binding sites for the ecdysone regulatory hierarchy early gene products E74 and BR-C, as well as transcription factors determining correct tissue- and stage-specific expression of GATA and HNF3/fkh. In situ hybridization demonstrated that in the ovaries of transgenic females DsRed mRNA was present in ovarian germ cells and nurse cells of mature ovarian follicles, together with VgR mRNA. In contrast, DsRed mRNA was absent in the oocyte that had a high level of endogenous VgR mRNA. Although the 1.5-Kb upstream region was sufficient to drive a high-level germ line cell-specific expression of the reporter, additional signals were required for translocation of exogenous mRNA from nurse cells into the oocyte.