Elucidation of Endocrinological Mechanisms during Tick Vitellogenesis

扁虱的卵黄发生似乎受蜕皮类固醇的调节。蜕皮类固醇可能通过与两个核受体--蜕皮类固醇受体(ECR)和维甲酸X受体(RXR)的异源二聚体形成复合体发挥作用。在以往的研究中，已交配的褐嘴鸟雌性在充血后表现出几个高蜕皮类固醇滴度和卵黄蛋白原(VG)合成和卵成熟的高峰，而处女雌性则表现出很低的蜕皮类固醇水平，没有峰值，VG合成水平较低，没有卵成熟。这些结果表明蜕皮类固醇在硬蜱VG合成和卵成熟的调节中起作用，但为了阐明这一作用，我们用实时荧光定量聚合酶链式反应比较了卵黄发生交配和处女的雌性硬蜱中ECR和RXR的表达模式。在交配和处女雌性中，ECR和RXR的表达在采血后不久都增加了。交配雌鼠ECR和RXR的表达与血淋巴中高的蜕皮类固醇滴度相一致。ECR和RXR在交配和处女雌性中的表达没有差异，只有交配的雌性蜕皮类固醇滴度增加，这进一步支持了VG合成和卵成熟受到蜕皮类固醇的调节。

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.