Differential expression and regulation by 20-hydroxyecdysone of mosquito ecdysteroid receptor isoforms A and B.
Cloning of the AaEcR-A isoform, along with the previously cloned AaEcR-B isoform, has permitted us to evaluate the expression of AaEcR isoforms during mosquito vitellogenesis. Mosquito EcR isoform transcripts exhibited dramatically different patterns of expression after a blood meal-triggered activation of vitellogenesis in the fat body. The AaEcR-B transcript level rose sharply by 4-h post blood meal (PBM), coinciding with the small ecdysteroid peak, and then declined reaching its lowest level at 16-24-h PBM. In contrast, the AaEcR-A transcript peaked at 16-20-h PBM, coinciding with the large ecdysteroid peak. AaEcR-B and AaEcR-A transcripts exhibited a striking difference in sensitivity to 20-hydroxyecdysone (20E), being maximally activated at 10(-8) and 10(-6) M, respectively. Both ecdysteroid receptor (EcR) isoform mRNAs were transcribed in a cycloheximide-independent manner, suggesting that they are direct targets of 20E. However, AaEcR-A transcription requires continuous presence of 20E, while AaEcR-B mRNA level rose for 4 h and then declined under the same conditions. These results indicate the mosquito EcR isoforms play distinct physiological functions during vitellogenesis in the mosquito fat body.
Wang
Sheng-Fu
SF
Program in Genetics, Michigan State University, East Lansing, MI 48824, USA.
Li
Chao
C
Sun
Guoqiang
G
Zhu
Jinsong
J
Raikhel
Alexander S
AS
D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D009033:Culicidae / Q000737:chemistry / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004441:Ecdysterone / Q000494:pharmacology*; D005260:Female; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects*; D007700:Kinetics; D008969:Molecular Sequence Data; D020033:Protein Isoforms; D012333:RNA, Messenger / Q000032:analysis / Q000096:biosynthesis; D011987:Receptors, Steroid / Q000096:biosynthesis* / Q000235:genetics; D014158:Transcription, Genetic / Q000187:drug effects; D014818:Vitellogenesis
D020033:Protein Isoforms; D012333:RNA, Messenger; D011987:Receptors, Steroid; C034808:ecdysteroid receptor; D004441:Ecdysterone