Elucidation of Ecdysteroid Regulated Mechanisms in Tick Reproduction

大多数银蛛科的雌性繁殖需要吸血。血粉似乎刺激后端器官产生脂肪体刺激因子（FSF），该因子被认为是一种表皮类固醇，以诱导卵黄蛋白原（Vg）的合成。我们对卵黄发生与卵外甾体激素关系的研究表明，体外甾体激素的生理水平升高可加速雄性摩巴雀鸟卵黄生成、诱导卵子成熟和促进产卵。目前对半代谢昆虫和较原始的节肢动物中表皮甾体的分子作用研究较少。因此，我们鉴定并分析了在moubata交配雌性和未交配雌性中外皮甾体受体（EcR）和类视黄醇X受体（RXR）的表达，以进一步阐明外皮甾体在蜱体内的调控机制。这些研究表明，山蛙的ecdysteroids （OmEcRA）受体与其他节肢动物的ecr具有较高的同源性，而OmRXR与硬蜱、甲壳类和脊椎动物的rxr具有较高的同源性，而与昆虫的rxr和USPs的rxr具有较高的同源性。在Vg合成和卵子成熟前，充血雌虫OmEcR和OmRXR的表达与体外类固醇滴度一致，但在交配雌虫和未交配雌虫之间存在一定差异。处女雌虫合成的Vg浓度要低得多，而且在整个生殖周期中，由于体外类固醇水平较低，卵子不太可能成熟，但处女雌虫的OmRXR表达高于交配雌虫。需要进一步的研究来解释交配和未交配雌性之间的这些差异。体外甾体/EcR/RXR复合物在软蜱卵黄形成的调控中起重要作用。

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.