Elucidation of Ecdysteroid Regulated Mechanisms in Tick Reproduction

大多数Argasidae雌性动物的繁殖都需要血餐。血餐似乎刺激后端的一个器官产生一种脂肪身体刺激因子(FSF)，这被认为是一种蜕皮类固醇，以诱导卵黄蛋白原(VG)的合成。我们对蜕皮激素与卵黄发生关系的研究表明，蜕皮激素的生理性升高加速了VG的合成，诱导了卵的成熟，并刺激了交配后的斑嘴鸟雌体的产卵。关于蜕皮激素在半代谢昆虫和更原始的节肢动物中的分子作用的研究很少。因此，我们鉴定和分析了蜕皮类固醇受体(ECR)和维甲酸X受体(RXR)在交配后和未交配雌体中的表达，以进一步阐明蜕皮类固醇在硬蜱中的调节机制。这些研究表明，野鼠蜕皮类固醇受体(OmEcRA)与其他节肢动物的ECR有很高的同源性，而OmRXR与硬蜱、甲壳类和脊椎动物的RXR有很高的同源性，而与昆虫的RXR和USPS没有很高的同源性。在VG合成和卵子成熟之前，充血雌虫OmEcR和OmRXR的表达与蜕皮激素滴度一致，但交配和处女雌虫之间存在一定的差异。处女雌性合成的VG浓度要低得多，卵子不太可能成熟，因为在整个生殖周期中蜕皮类固醇水平很低，但处女雌性的OmRXR表达高于交配的雌性。需要进一步的研究来解释交配和处女雌性之间的这些差异。蜕皮激素/ECR/RXR复合体在软蜱卵黄发生的调控中起着重要作用。

A blood meal is required for reproduction in most Argasidae females. The blood meal appears to stimulate an organ in the posterior end to produce a fat body stimulating factor (FSF), which is thought to be an ecdysteroid, to induce vitellogenin (Vg) synthesis. Our studies on the relationship of vitellogenesis and ecdysteroids indicate that physiological elevation of ecdysteroids accelerates Vg synthesis, induces egg maturation and stimulates oviposltion in fed mated Ornithodoros moubata females. There are few studies on the molecular actions of ecdysteroids in hemimetabolous insects and more primitive arthropods. Therefore, we identified and analyzed the expression of the ecdysteroid receptor (EcR) and retinoid X receptor (RXR) in O. moubata mated and virgin females to further elucidate the ecdysteroid regulated mechanisms in ticks. These studies revealed the ecdysteroid (OmEcRA) receptor from O. moubata has high homology with EcRs of other arthropods, whereas OmRXR showed high homology to hard tick, crustacean and vertebrate RXRs rather than insect RXRs and USPs. OmEcR and OmRXR expression coincided with ecdysteroid titers in engorged females before Vg synthesis and egg maturation but there were some differences between mated and virgin females. Virgin females synthesize much lower concentrations of Vg and egg maturation does not occur likely because of low levels of ecdysteroids throughout the reproductive cycle, but OmRXR expression in virgin females is higher than in mated females. Further studies are needed to explain these differences between mated and virgin females. The ecdysteroid/EcR/RXR complex appears to be important in the regulation of vitellogenesis of soft ticks.