Evidence for expression of EcR and USP components of the 20-hydroxyecdysone receptor by a mosquito cell line

The reverse transcriptase polymerase chain reaction (RT-PCR) was used to examine whether the C7-10 cell line from the mosquito, Aedes albopictus, expresses transcripts encoding 20-hydroxyecdysone receptor (EcR) and ultraspiracle (USP) isoforms known to constitute a functional 20-hydroxyecdysone receptor. Here we describe recovery and analysis of products with high similarity to the EcR and to the USP isoform "a" that have been reported from the related mosquito, Aedes aegypti. The C7-10 EcR was 97% identical to Aedes aegypti EcR in amino acid sequence. Key features of the nuclear/steroid hormone receptor superfamily, including the zinc fingers, proximal (P)-box, and distal (D)-box were well conserved. However, the C7-10 EcR contained 5 additional amino acids in the C-terminal domain F, which required introduction of gaps to maximize alignment. The 5'-untranslated regions of the two mosquito EcRs were 98% identical, but the function of this region remains unknown. The C7-10 USP was 95% identical in amino acid sequence to the longer Aedes aegypti isoform "a." Although only the C7-10 EcR was detected on Northern blots using total RNA from the cell line, transcripts for both EcR and USP were detected using the RT-PCR procedure. These transcripts appeared to be expressed constitutively and expression levels were not affected by treatment of cells with 20-hydroxyecdysone. Arch.