cDNA cloning and transcriptional regulation of the vitellogenin receptor from the imported fire ant, Solenopsis invicta Buren (Hymenoptera: Formicidae)

摘要

Receptors that transport vitellogenin into oocytes are of vital importance to egg-laying species because they promote oocyte development. In this study, we describe the cloning of the first hymenopteran vitellogenin receptor (VgR) cDNA. Using reverse transcription polymerase chain reaction (RT-PCR) and both 5?- and 3?- rapid amplification of cDNA ends (RACE), cDNA fragments encompassing the entire coding region of a putative VgR from fire ant (= SiVgR) were cloned and sequenced. The complete SiVgR cDNA has a length of 5764 bp encoding a 1782-residue protein with a predicted molecular mass of 201.3 kDa. The deduced amino acid sequence of the SiVgR revealed that it encoded a protein belonging to the low-density lipoprotein receptor superfamily. The number and arrangement of modular domains of SiVgR are the same as those of mosquito and fruit fly VgRs, except there are only four Class A cysteine-rich repeats in the first ligand binding domain of SiVgR compared to five in the mosquito and fruit fly. The deduced amino acid sequence of the SiVgR exhibited 35% and 31% identity to those of the mosquito and fruit fly VgRs, respectively. Northern blot analysis demonstrated that the 7.4-kb SiVgR mRNA was present only in Northern blot analysis demonstrated that the 7.4-kb SiVgR mRNA was present only in ovaries of reproductive females − both alates (virgins) and queens (mated) and was more abundant in alates. The developmental profile of transcriptional expression was determined by semiquantitative RT-PCR. It showed that the SiVgR transcript increased 6-fold from 0- to 10-days after mating, then remained constant through 30 days. It also showed that the SiVgR transcripts increased with age in alate virgin females. The transcriptional expression of the SiVgR was up-regulated more than two-fold by methoprene, a juvenile hormone analog, as determined by using an in vitro system. This suggested the SiVgR gene is JH regulated.