Organization and developmental expression of the mosquito vitellogenin receptor gene

Vitellogenin is a precursor of the major yolk protein, vitellin. It is inte rnalized by developing oocytes via receptor-mediated endocytosis. Previousl y, we characterized the vitellogenin receptor (VgR) from oocytes of the mos quito Aedes aegypti [Sappington, T.W., Kokoza,V.A., Cho,W.L. and Raikhel, A .S. (1996) Molecular characterization of the mosquito vitellogenin receptor reveals unexpected high homology to the Drosophila yolk protein receptor. Proc Natl Acad Sci USA 93: 8934-8939]. The VgR receptor has a unique struct ure with two putative ligand-binding domains. In order to understand the re gulation of this important molecule, we characterized the VgR gene structur e and its expression during vitellogenesis in the mosquito A. aegypti. We r eport here that the VgR gene was separated by five introns that have an ave rage length of 60 bp, except for the second intron which was more than 20 k b long. Most introns were located within the coding regions of the first pr otein domain. We isolated two allelic variations of the VgR gene, VgR1 and VgR2, the nucleotide sequences of which differing only in their 5'-flanking regions. Considering their frequency in the mosquito genome, VgR2 appeared to be a major allele. The expression of VgR mRNA was studied by the Northe rn blot analysis and in situ hybridization. The level of the VgR transcript started to rise in the ovary one day post-eclosion. It continued its drama tic rise during the vitellogenic period, reaching its peak at 24 h PBM. The VgR transcript was present exclusively in ovaries where it was seen in ooc ytes and nurse cells of primary follicles and germ-line cells of the germar ium.