A COUP-TF/Svp homolog is highly expressed during vitellogenesis in the mosquito Aedes aegypti

Abstract

In the mosquito Aedes aegypti, vitellogenesis is activated via an ecdysteroid hormonal cascade initiated by a blood meal. The functional ecdysone receptor is a heterodimer composed of the ecdysone receptor (EcR) and ultraspiracle, the homolog of the retinoid X receptor. The precise tuning of this hormonal response requires participation of both positive and negative transcriptional regulators. In Drosophila, Svp, a homolog of chicken ovalbumin upstream promoter transcription factor (COUP-TF), inhibits ecdysone receptor complex-mediated transactivation in vitro and in vivo. Here we report the cloning and characterization of the Svp homolog in mosquito Aedes aegypti, AaSvp. It possesses a high degree of amino acid sequence similarity to the members of the COUP-TF/Svp subfamily. AaSvp transcripts and protein are present in the fat body at high levels from the state of arrest to about 60 h post blood meal. AaSvp binds strongly to a variety of direct repeats of the sequence AGGTCA, but weakly to inverted repeats such as hsp27EcRE. Transient transfection assays in Drosophila S2 cells showed that AaSvp was able to repress 20-hydroxyecdysone (20E)-dependent transactivation mediated by the mosquito ecdysteroid receptor complex. These data suggest that AaSvp negatively regulates the 20E signaling in the fat body during mosquito vitellogenesis.

Juvenile hormone biosynthesis in adult Blattella germanica requires nuclear receptors Seven-up and FTZ-F1

“…In addition to the functions described, Svp also exerts regulatory functions in holometabolous insects through the attenuation of the activity of the 20E-signalling cascade by inhibiting the normal functioning of the EcR-USP heterodimer4950. In A. aegypti , AaSvp interacts with AaUSP at the end of the vitellogenic cycle inhibiting the 20E-dependent transactivation of target genes such as AaVg 5152.…”

Four-way regulation of mosquito yolk protein precursor genes by juvenile hormone-, ecdysone-, nutrient-, and insulin-like peptide signaling pathways

“…After a blood meal and in the presence of 20E, EcR displaces AHR38 and forms a heterodimer with USP. Sevenup (Svp), a mosquito homolog of chicken ovalbumin upstream transcription factor, acts as a transcriptional repressor by binding directly to AGGTCA repeats within the ecdysone response elements of the vg-1 promoter, thereby inhibiting the ecdysone responsiveness of these promoters (Miura et al, 2002). …”

COUP-TFs and eye development

“…Since the identification of human COUP-TF genes [2–8], their homologs have been cloned from many other organisms, including mCOUP-TFI and -TFII from mice [44, 45], rCOUP-TFI from rats [46], xCOUP-TFA , -TFB and -TFC from Xenopus [47–49], cCOUP-TFII from chicken [50], bCOUP-TFI and -TFII from bovine [51], the seven-up gene ( svp ) from Drosophila [52], the svp [40], svp [44] and svp [46] genes from zebrafish [53, 54], spCOUP-TF from sea urchin [55], and AaSvp in mosquito Aedes aegypti [56]. Their sequences reveal that COUP-TF genes are highly conserved from human to invertebrate [49].…”