Molecular cloning and developmental expression pattern of the vitellogenin receptor from the cockroach, Leucophaea maderae

Abstract

A cDNA encoding the vitellogenin receptor (VgR) of the cockroach, Leucophaea maderae (Lm) was cloned and sequenced. The coding region consisted of 5454bp flanked by a 67bp 5'-untranslated region (UTR) and a 168bp 3'-UTR, which encoded a 1792-residues mature protein with a predicted molecular mass of 199.84kDa. The deduced amino acid sequence of the LmVgR cDNA revealed two ligand-binding domains with 5 repeats in the first domain and 8 in the second domain similar to those of other insect VgRs. Northern hybridization analysis revealed the presence of a approximately 7.3kb transcript that was specifically expressed only in the ovarian tissues. The developmental expression profile demonstrated that LmVgR mRNA exists throughout the ovarian development, and that the transcriptional level is especially high in the previtellogenic periods. The Immunoblot analysis detected an ovary-specific VgR protein with a M(r) of approximately 215kDa under reducing conditions. The VgR protein continues to increase until day 3 of adult emergence, declines thereafter slightly until day 6, then rises again and reaches to its maximum on day 9 during the vitellogenic periods. Compared to other insect VgRs, the LmVgR primary protein structure shows an overall amino acid identity between 33% and 65% to their corresponding gene products. The similarity was high when compared with other cockroach VgRs described from Periplaneta americana (55%) and Blattella germanica (65%). A proposed phylogenetic (neighbor-joining) relationship suggests that LmVgR and B. germanica VgR have closer ancestry than from P. americana VgR. The cytoplasmic tail of LmVgR contains a leucine-isoleucine internalization signal similar to other insect counterparts unlike the NPXY motif of other LDLR family members. The cockroaches VgRs harbor, in addition, a putative NPTF motif for internalization. The sequence reported in this paper has been submitted to GenBank (accession number: ).