Ecdysteroid Regulation of Ovarian Growth and Oocyte Maturation in the Red Flour Beetle, Tribolium castaneum

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 4th 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