Student Activities 2012-2013

Derek Tokar

Vitellogenin RNAi treatment halts oocyte growth without decreasing protein translation

Activity:
Society for Integrative and Comparative Biology Annual Meeting

Abstract:

 Organisms must allocate resources to either somatic storage or reproduction, yet the physiological mechanisms coordinating this trade-off are poorly understood. In the lubber grasshopper, vitellogenin (Vg) is the precursor protein to vitellin, which constitutes 90% of protein in mature oocytes. Previously, to investigate how investment into somatic storage is affected by reproductive protein resources, we utilized RNA interference (RNAi), reducing Vg-mRNA in the fat body 30-fold, however Vg protein in the hemolymph increased.  Additionally, Vg-RNAi treatment halted ovarian growth and doubled fat body mass. In this study, we measured hemolymph levels of 90 kDa hexameric storage protein (Hex90), ovarian vitellin content, and rates of Vg production by the fat body. We compared Vg-RNAi treated individuals to Hex90-RNAi or buffer-injected controls by injecting dsRNA before vitellogenesis and sampling from early to late vitellogenesis. Hex90-RNAi treatment reduced Hex90 levels when compared to the buffer-injected and Vg-RNAi groups combined (P=0.04). The Vg-RNAi group had significantly lower vitellin content per gram of ovary compared to buffer-injected (P=0.006), but not the Hex90-RNAi (P=0.360) group, indicating that Vg-RNAi treatment may prevent Vg from being sequestered into developing oocytes. In addition, rate of Vg production by the fat body was higher at 19 d than at 26 d (P=0.002) but was not affected by Vg-RNAi treatment (P=0.383). Together, these results suggest that Vg-RNAi treatment does not reduce the translation rate of Vg-mRNA, but nonetheless halts sequestration of Vg into developing oocytes and increases fat body mass, consistent with a trade-off between reproduction and storage.