C. Li et al., Conserved molecular mechanism for the stage specificity of the mosquito vitellogenic response to ecdysone, DEVELOP BIO, 224(1), 2000, pp. 96-110
In the mosquito Aedes aegypti, the adult female becomes competent for a vit
ellogenic response to ecdysone after previtellogenic development. Here, we
show that beta FTZ-F1, the nuclear receptor implicated as a competence fact
or for stage-specific responses to ecdysone during Drosophila metamorphosis
, serves a similar function during mosquito vitellogenesis. AaFTZ-F1 is exp
ressed highly in the mosquito fat body during pre- and postvitellogenic per
iods when ecdysteroid titers are low. The mosquito AaFTZ-F1 transcript near
ly disappears in mid-vitellogenesis when ecdysteroid titers are high. An ex
pression peak of HR3, a nuclear receptor implicated in the activation of be
ta FTZ-P1 in Drosophila, precedes each rise in mosquito FTZ-F1 expression.
In in vitro fat body culture, AaFTZ-F1 expression is inhibited by 20-hydrox
yecdysone (20E) and superactivated by its withdrawal. Following in vitro Aa
FTZ-F1 superactivation, a secondary 20E challenge results in superinduction
of the early AaE75 gene and the late target VCP gene. Electrophoretic mobi
lity-shift assays show that the onset of ecdysone-response competence in th
e mosquito fat body is correlated with the appearance of the functional AeF
TZ-F1 protein at the end of the previtellogenic development. These findings
suggest that a conserved molecular mechanism for controlling stage specifi
city is reiteratively used during metamorphic and reproductive responses to
ecdysone. (C) 2000 Academic Press.