MARTIN, T.R.; JASKOWIAK, K.M.; FEI, H.; HATLE, J.D.; BORST, D.W.: The physiological effects of starvation on vitellogenesis in the lubber grasshopper

Previous studies with the lubber grasshopper, Romalea microptera, have shown that starvation inhibits oocyte growth. Since this effect may involve vitellogenesis, we studied its regulation during acute starvation. Adult females were collected at eclosion, maintained under well-fed conditions, and moved to individual containers after 15 days (shortly after the onset of vitellogenesis). At 17 days, half of the animals were starved. Hemolymph samples were collected from each individual every 48 hr from 15 to 23 days. Six to eight animals were killed after each bleeding. A portion of their fat body was incubated in vitro for 4 hr to determine (by ELISA) the amount of Vg released into the culture medium. RNA was extracted from the remaining fat body tissue, converted to cDNA, and analyzed by real-time PCR to determined Vg transcript levels (normalized to levels of β-actin mRNA). Starvation strongly decreased the in vitro production of Vg, dropping it to 19% of control levels at 48 hr (P < 0.0021). Starvation nonsignificantly reduced hemolymph levels of Vg and JH to 49% and 29%, respectively, of control levels at 48 hr. Hemolymph levels of Vg did not decrease further during prolonged starvation, suggesting that Vg uptake by the oocytes was reduced. Fat body levels of Vg-transcript in starved animals were similar to the levels measured in control animals (P<0.731). Hence, the decrease in Vg production appears to reflect a decrease in the translation or release of Vg, since levels of Vg-transcript remained high. These results fit a model in which both Vg production and uptake can be controlled. Acute effects on Vg production appear to involve the down-regulation of translation. (Supported by NSF grant DBI 9978810 to DWB).