Differential expression and regulation by 20-hydroxyecdysone of mosquito ultraspiracle isoforms.
Ultraspiracle (USP), the insect homologue of the vertebrate retinoid X receptor, is an obligatory dimerization partner for the ecdysteroid receptor (EcR). Two USP isoforms, USP-A and USP-B, with distinct N-termini, occur in the mosquito Aedes aegypti. In the fat body and ovary, USP-A mRNA is highly expressed during the pre- and late vitellogenic stages, corresponding to a period of low ecdysteroid titer, while USP-B mRNA exhibits its highest levels during the vitellogenic period, correlating with a high ecdysteroid titer. Remarkably, 20-hydroxyecdysone (20E) has opposite effects on USP isoform transcripts in in vitro fat body culture. This steroid hormone upregulates USP-B transcription and its presence is required to sustain a high level of USP-B expression. In contrast, 20E inhibits activation of USP-A transcription. Although EcR.USP-A recognizes the same ecdysteroid-responsive elements, EcR.USP-B binds them with an affinity twofold higher than that of EcR.USP-A. Likewise, EcR.USP-B transactivates a reporter gene in CV-1 cells twofold more strongly than EcR.USP-A. These results suggest that USP-B functions as a major heterodimerization partner for EcR during the vitellogenic response to 20E in the mosquito.
Wang
S F
SF
Department of Entomology, Michigan State University, East Lansing, Michigan, 48824, USA.
Li
C
C
Zhu
J
J
Miura
K
K
Miksicek
R J
RJ
Raikhel
A S
AS
D000330:Aedes / Q000254:growth & development*; D000818:Animals; D001665:Binding Sites; D003513:Cycloheximide / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000235:genetics*; D019281:Dimerization; D029721:Drosophila Proteins; D004441:Ecdysterone / Q000494:pharmacology*; D005216:Fat Body / Q000378:metabolism; D005260:Female; D018507:Gene Expression Regulation, Developmental; D009924:Organ Culture Techniques; D010053:Ovary / Q000378:metabolism; D011485:Protein Binding; D020033:Protein Isoforms / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis; D011987:Receptors, Steroid / Q000096:biosynthesis / Q000235:genetics*; D012091:Repetitive Sequences, Nucleic Acid; D014018:Tissue Distribution; D014157:Transcription Factors / Q000096:biosynthesis / Q000235:genetics*; D015533:Transcriptional Activation / Q000187:drug effects; D014818:Vitellogenesis / Q000187:drug effects / Q000235:genetics*
D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D020033:Protein Isoforms; D012333:RNA, Messenger; D011987:Receptors, Steroid; D014157:Transcription Factors; C066030:USP protein, Drosophila; D004441:Ecdysterone; D003513:Cycloheximide