Abstract
Ecdysteroid hormones influence the development and reproduction of arthropods by binding a heterodimeric complex of nuclear receptors, the ecdysone receptor (EcR) and the retinoid-X-receptor/ultraspiracle (RXR/USP). Here, we report on the in vivo role(s) of the ecdysone receptor complex, SchgrEcR/SchgrRXR, in the female reproductive physiology of a major phytophagous pest insect, i.e. the desert locust, Schistocerca gregaria. Tissue and temporal distribution profiles were analysed during the first gonadotrophic cycle of adult female locusts. RNA interference was used as a reverse genetics tool to investigate the in vivo role of the ecdysone receptor complex in ovarian maturation, oogenesis, fertility and fecundity. We discovered that silencing the ecdysone receptor complex in S. gregaria resulted in impaired ovulation and oviposition, indicative for a crucial role of this complex in chorion formation. We also found evidence for a feedback of SchgrEcR/SchgrRXR on juvenile hormone biosynthesis by the corpora allata. Furthermore, we observed a tissue-dependent effect of the SchgrEcR/SchgrRXR knockdown on the transcript levels of the insulin receptor and neuroparsin 3 and 4. The insulin receptor transcript levels were upregulated in the brain, but not the fat body and gonads. Neuroparsins 3 and 4 transcript levels were down regulated in the brain and fat body, but not in the gonads.
Highlights
Ecdysteroids and juvenile hormones (JHs) are two major insect hormone families famous for their roles in development, moulting and metamorphosis
The tissue distribution profile has been studied in the thoracic ganglia (TG), corpora cardiaca (CC), suboesophageal ganglion (SOG), salivary gland (Salgl), prothoracic glands (PG), fat body (Fb), midgut (MG), and ovaries (Ov) of 10-day-old female adult locusts and the testes and accessory glands (AG) of 10-day-old male adult locusts (Fig. 1A,B)
The highest transcript levels of SchgrEcR were found in the fat body of 10-day-old female adult locusts (Fig. 1A), while the highest transcript levels of SchgrRXR were found in the corpora allata (CA), the thoracic ganglia (TG) and the ovaries of 10-day-old female adult locusts, as well as in the testes of 10-day-old male adult locusts (Fig. 1B)
Summary
Ecdysteroids and juvenile hormones (JHs) are two major insect hormone families famous for their roles in development, moulting and metamorphosis. In Schistocerca gregaria, the Halloween genes spook (SchgrSpo), phantom (SchgrPhm) and shade (SchgrShd) were previously characterised in fifth nymphal locusts[11,12] In addition to their regulatory role in insect moulting, ecdysteroids are necessary in different aspects of female reproductive physiology. Research on the regulation of ovarian maturation and oogenesis in more primitive insect orders with panoistic ovaries has seriously lagged behind on that in Holometabola with meroistic ovaries, with only a few studies performed in the cockroach species, Blattella germanica, the German cockroach, and Diploptera punctata, the Pacific beetle cockroach[25,26,27], and in the house cricket, Acheta domesticus[28] In both Orthoptera and Dictyoptera, JH acts as the primary regulator of ovarian development and ecdysteroid titres significantly increase at the end of oogenesis[1,28,29,30,31]. We investigated the effect of the SchgrEcR/SchgrRXR knockdown on the transcript levels of different genes of interests, belonging to the previously mentioned hormonal pathways
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