Molecular Mechanisms Regulating Tick Vitellogenesis

我们的研究集中在卵黄蛋白原（Vg）的特性和阐明的机制，调节这种蛋白质在软蜱的表达。在脂肪体中合成的Vg由血淋巴携带到卵巢，并作为卵黄蛋白（Vn）掺入卵母细胞。以往的研究表明，卵黄发生诱导因子（VIF）和脂肪体刺激因子（FSF）调节Vg的合成。VIF是一种肽，FSF似乎是一种类固醇。注射高浓度的蜕皮激素刺激未进食的雌性的Vg tilers增加。对未交配和交配的进食雌性的血淋巴、全身和生殖道中的蜕皮类固醇滴度进行分析，表明蜕皮类固醇调节蜱的生殖。蜕皮激素和Vg浓度保持在低水平，卵母细胞不成熟，没有产卵发生在处女女性。另一方面，在交配雌性血淋巴和全身提取物中分别观察到三个和四个不同的蜕皮类固醇峰。第一个峰与FSF分泌的开始一致。第二，一个大的宽峰，与吸收Vg到卵母细胞。第三个高峰是一个小高峰，出现在产卵开始时。第四个大的宽峰，仅在整个身体，似乎是由于蜕皮类固醇在生殖道。实验正在进行中，以确定蜕皮类固醇（EcR）和维甲酸X（RXR）受体的O。穆巴塔这些研究表明，在这种蜱中至少有三种蜕皮类固醇受体（EcR）亚型。蜕皮激素受体基因在卵黄发生不同阶段的表达正在研究中。卵黄蛋白原基因的全序列尚未完全分析，但完成后将使我们能够确定该基因是否具有蜕皮激素反应元件，并更仔细地研究卵黄发生。

Our research has concentrated on characterization of vitellogenin (Vg) and elucidation of mechanisms regulating the expression of this protein in a soft tick. Vg synthesized in the fat body is carried by the hemolymph to the ovary and incorporated into the oocytes as vitellin (Vn). Previous studies have shown two factors, vitellogenesis-inducing factor (VIF) and fat body stimulating factor (FSF), regulate Vg synthesis. VIF is a peptide and FSF appears to be a steroid. Injection of high concentrations of ecdysteroids stimulates an increase in Vg tilers of unfed females. Analysis of ecdysteroid titers in the hemolymph, whole body and reproductive tracts of virgin and mated fed females indicate ecdysteroids regulate reproduction in ticks. Ecdysteroid and Vg concentrations remain at low levels, oocytes do not mature and no oviposition occurs in virgin females. On the other hand, three and four distinct ecdysteroid peaks are seen in mated female hemolymph and whole body extracts, respectively. The first peak coincides with the beginning of FSF secretion. The second, a large broad peak, coincides with absorption of Vg into the oocytes. The third peak, a small peak, occurs at the start of oviposition. The fourth large broad peak, only in the whole body, appears to be due to ecdysteroids in the reproductive tract. Experiments are underway to identify the ecdysteroid (EcR) and retinoid X (RXR) receptors of O. moubata. These studies indicate there are at least three isoforms of ecdysteroid receptors (EcR) in this tick. Expression of the ecdysteroid receptor genes during the different phases of vitellogenesis is under investigation now. The full sequence of the vitellogenin gene has not yet been completely analyzed, but when completed will allow us to determine if this gene has an ecdysteroid responsive element and to investigate vitellogenesis more carefully.