Elucidation of Endocrinological Mechanisms during Tick Vitellogenesis

卵黄发生似乎是由蜱蜕皮类固醇调节。蜕皮甾体可以通过与两个核受体（蜕皮甾体受体（EcR）和类维生素A X受体（RXR））的异源二聚体形成复合物来发挥作用。在以前的研究中，交配雌性的鸟喙龙表现出几个峰值的高蜕皮类固醇滴度与卵黄蛋白原（Vg）的合成和卵成熟后饱食，而处女雌性表现出非常低水平的蜕皮类固醇没有峰值，较低水平的Vg合成和没有卵成熟。这些结果表明蜕皮甾体在调节蜱Vg合成和卵成熟中的作用，但为了阐明这种作用，我们通过实时PCR比较了卵黄发生交配和处女雌性蜱中的EcR和RXR表达模式。在交配和处女雌性动物中，吸血后EcR和RXR的表达均迅速增加。EcR和RXR在交配雌性中的表达与血淋巴中蜕皮激素的高滴度相一致。在交配和处女女性的蜕皮激素滴度增加，只有交配女性的EcR和RXR的表达缺乏差异提供了进一步的支持，Vg合成和卵子成熟的蜕皮激素调节。

Vitellogenesis appears to be regulated by ecdysteroids in ticks. Ecdysteroids may function by forming a complex with a heterodimer of two nuclear receptors, ecdysteroid receptor (EcR) and retinoid X receptor (RXR). In previous studies, mated females of Ornithodoros moubata showed several peaks of high ecdysteroid titers with vitellogenin (Vg) synthesis and egg maturation after engorgement, whereas virgin females showed very low levels of ecdysteroids with no peaks, lower levels of Vg synthesis and no egg maturation. These results indicate a role for ecdysteroids in the regulation of tick Vg synthesis and egg maturation but in order to clarify this role in O.moubata we compared the EcR and RXR expression patterns in vitellogenic mated and virgin female ticks by real-time PCR. EcR and RXR expression increased soon after blood feeding in both mated and virgin females. EcR and RXR expression in mated females coincided with the high ecdysteroid titers in hemolymph. A lack of differences in EcR and RXR expression in mated and virgin females with increased ecdysteroid titers in only mated females provides further support that Vg synthesis and egg maturation are regulated by ecdysteroids.