Analysis of tissues for EcR and RXR nuclear receptor gene expression during vitellogenesis in the soft tick Ornithodoros moubata

Abstract

Vitellogenin (Vg) synthesis and oocyte development appear to be induced by ecdysteroids in the soft tick Ornithodoros moubata. Vg transcription in insects has been shown to be mediated by two nuclear receptors, an ecdysteroid receptor (EcR) and a retinoid X receptor (RXR). EcR and RXR expression in female ticks increase after engorgement. However, there is little information about EcR and RXR expression in tissues as related to reproduction. Therefore, the sites of EcR and RXR expression during vitellogenesis were determined. Expression levels of EcR and RXR were determined for salivary glands, midgut, ovary, anterior reproductive tract, fat body, muscle, and cuticle of mated females by reverse transcriptase RT-PCR and real-time PCR. Ovaries showed constant expression of EcR and RXR throughout the adult female stage. The fat body showed higher expression of EcR and RXR on one day after engorgement. The fat body of female ticks has been reported to be the organ of Vg synthesis. Therefore, increases in EcR and RXR of the fat body support the hypotheses that the site of Vg synthesis is the fat body and ecdysteroids regulate this synthesis in O. moubata. EcR and RXR in the ovary and anterior reproductive tract may also play roles in the regulation of oocyte development.