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A schematic representation of the 20E regulated events during the first vitellogenic cycle in the fat body of the mosquito A. aegypti.

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posted on 26.09.2012, 02:39 by Daniel Mane-Padros, Josefa Cruz, Andrew Cheng, Alexander S. Raikhel

After a blood meal activation, a high level of 20E acts via EcRA/USPB heterodimer activating early genes, BrZ2, E74B and E75A, which synergistically activate late genes such as Vg [15][18]. TOR, activated by amino acids and insulin, is essential for activating late genes [3], [6]. TOR is also involved in inhibition of the programmed autophagy during vitellogenesis [19]. HR3 is inhibited by E75A [18], but activated by EcRA/USPB ensuring its timely expression. At the termination time, lowering of the 20E titer results in repressive action of BriZ1 (not shown) and BrZ4 on late genes such as Vg [15], [17]. In this study, we have shown that HR3 is involved in inhibition of late target genes expression (Vg). On the other hand, HR3 activates the EcRB/USPA heterodimer. EcR has been shown to repress TOR and activate autophagy [19]. We postulate that it is the EcRB/USPA heterodimer that is responsible for these functions mediating action of HR3; however, this link requires additional confirmation. HR3 acts as an activator of betaFTZ-F1 that in turn is essential for maintaining cyclicity of egg development. The green ovals – EcR/USP 20E heterodimeric receptor; blue boxes – genes that encode 20E regulated transcription factors (early genes); purple boxes – Target-of Rapamycin; black boxes – autophagy; orange boxes – late target genes. Green arrows depict activating effects and red lines - repressive effects. The basics of the scheme were adapted from [46]for comparison reasons.