Dubrovsky Edward B, Dubrovskaya Veronica A, Berger Edward M
Department of Biology, Dartmouth College, Hanover, NH 03755, USA.
Dev Biol. 2004 Apr 15;268(2):258-70. doi: 10.1016/j.ydbio.2004.01.009.
Ecdysone and juvenile hormone (JH) are important regulators of insect growth and development. While ecdysone initiates a transition from one developmental stage to another, JH determines the nature of the transition. How these two hormones interact at the molecular level is not known. Here we report the JH inducibility of the E75A nuclear receptor encoded by the E75 early ecdysone-inducible gene. In Drosophila S2 cells, E75A transcription is specifically activated by JH at concentrations well within the physiological range found in larvae and adults. The induction is rapid and does not require a concurrent protein synthesis, and thus represents a primary hormone response. Consistent with JH regulation, E75A mRNA levels are reduced in ovaries of apterous(4) mutant adults defective in JH secretion. Expression is rescued by topical methoprene application. We further provide evidence that ectopic E75A is sufficient to perform several functions in the JH signaling pathway. First, it can down-regulate its own transcription. Second, E75A can potentiate the JH inducibility of a secondary response gene, JhI-21. Finally, in the presence of JH, E75A can repress ecdysone activation of early genes including Broad-Complex. Based on these data, we propose a model for the role of E75A in the ecdysone-JH regulatory interplay.
蜕皮激素和保幼激素（JH）是昆虫生长发育的重要调节因子。虽然蜕皮激素启动从一个发育阶段到另一个发育阶段的转变，但保幼激素决定转变的性质。这两种激素在分子水平上如何相互作用尚不清楚。在此，我们报道了由E75早期蜕皮激素诱导基因编码的E75A核受体的保幼激素诱导性。在果蝇S2细胞中，E75A转录在幼虫和成虫生理范围内的浓度下被保幼激素特异性激活。这种诱导迅速，不需要同时进行蛋白质合成，因此代表了一种初级激素反应。与保幼激素调节一致，在保幼激素分泌有缺陷的无翅（4）突变体成虫的卵巢中，E75A mRNA水平降低。通过局部应用烯虫酯可恢复其表达。我们进一步提供证据表明，异位表达的E75A足以在保幼激素信号通路中发挥多种功能。首先，它可以下调自身转录。其次，E75A可以增强次级反应基因JhI-21的保幼激素诱导性。最后，在保幼激素存在的情况下，E75A可以抑制包括Broad-Complex在内的早期基因的蜕皮激素激活。基于这些数据，我们提出了一个关于E75A在蜕皮激素-保幼激素调节相互作用中作用的模型。
