Mosquito ecdysteroid receptor: analysis of the cDNA and expression during vitellogenesis.

An insect steroid hormone, 20-hydroxyecdysone (20E), plays an important role in regulating egg maturation in mosquitoes. To better understand its role, we cloned the cDNA coding for the putative ecdysteroid receptor from the mosquito, Aedes aegypti (AaEcR). The 4158 bp AaEcR cDNA has an open reading frame of 675 amino acids with 10 potential glycosylation sites and a putative phosphorylation polyserine domain. The AaEcR has a DNA binding domain with two zinc fingers and a ligand binding domain characteristic of members of the steroid hormone receptor superfamily. These AaEcR domains share 97 and 87% identities with the respective domains of the Drosophila ecdysteroid receptor (DmEcR). However, the A/B region of the AaEcR shares 35% identity with that of DmEcR-B1 isoform. The F region, located at the carboxyl-terminal of the AaEcR, has only 9% identity with the corresponding region of DmEcR. Potential nuclear targeting and dimerization signals are also present in the AaEcR sequence. There are three AaEcR transcripts of 4.2 kb, 6 kb and 11 kb in adult mosquitoes. 4.2 kb mRNA is predominantly expressed in female mosquitoes during vitellogenesis. In both the fat body and ovaries of the female mosquito, the level of AaEcR mRNA is high at the previtellogenic period and after the onset of vitellogenesis (6 h post blood meal, PBM).