Ecdysteroid regulation of ovarian growth and oocyte maturation in the red flour beetle, Tribolium castaneum

Abstract

Previous studies from our laboratory showed the involvement of juvenile hormone (JH) and ecdysteroid signaling in the regulation of female reproduction in the red flour beetle, Tribolium castaneum. JH regulates vitellogenin (Vg) synthesis in the fat body but the role of ecdysteroid signaling is not known. Here, we report on ecdysteroid regulation of ovarian growth and oocyte maturation. Microarray analysis of RNA isolated from ovaries showed the up-regulation of several genes coding for proteins involved in ecdysteroid signaling on the 4 th day after female adult eclosion. The functional analyses of genes coding for proteins involved in ecdysteroid and JH signaling pathways by RNA interference (RNAi) revealed that ecdysteroids but not JH regulate ovarian growth and primary oocyte maturation. Ultrastructural studies showed the temporal sequences of key events in oogenesis including the development of primary oocytes, the differentiation and development of follicle epithelial cells, and the formation of intercellular spaces to facilitate uptake of Vg protein. RNAi studies showed that ecdysone receptor (EcR) and ultraspiracle (USP) are required for the ovarian growth, primary oocyte maturation and the growth and migration of the follicle cells. These studies suggest important roles for ecdysteroids in the regulation of oocyte maturation in the beetle ovaries.

Molecular characterisation of the salmon louse, Lepeophtheirus salmonis salmonis (Krøyer, 1837), ecdysone receptor with emphasis on functional studies of female reproduction

“…Similar observations were reported from EcR knock-down studies of T. castaneum, where a 50-75% reduction in the vitellogenin transcript level resulted in a decrease in egg development (Xu et al, 2010). Moreover, development of a follicular cell layer necessary for oocyte maturation was disrupted, resulting in an arrest of the oocyte in the pre-vitellogenic stage (Parthasarathy et al, 2010). The same observations had previously been recorded in D. melanogaster where EcR deficiency resulted in abnormal egg chamber development and loss of vitellogenic stages (Carney and Bender, 2000).…”

Eat to reproduce: a key role for the insulin signaling pathway in adult insects

“…In the adult stage, ecdysteroids are mainly synthesized in the gonads (Brown et al, 2009), although other tissues have been suggested as additional sources of ecdysteroids in some insect species (e.g., Delbecque et al, 1990; Gillot and Ismail, 1995). Ecdysteroids have autocrine and paracrine regulatory roles in ovary and oocyte development, since they control ovary morphogenesis, differentiation of germ line stem cells and development of follicle cells (Parthasarathy et al, 2010; Gancz et al, 2011; Konig et al, 2011; Ting, 2013). In addition, conjugates are stored in the eggs as an embryonic source of ecdysteroids.…”

Juvenile Hormone Regulates Vitellogenin Gene Expression through Insulin-like Peptide Signaling Pathway in the Red Flour Beetle, Tribolium castaneum

“…cDNA synthesis and qRT-PCR reactions were performed using the genespecific primers (reported in Refs. 19 -21 or shown in Table 1) and methods described previously (19,20). Ribosomal protein gene rp49 was used as an internal control in qPCR analysis.…”