Apolipophorin III levels in Locusta migratoria. Developmental regulation of gene expression and hemolymph protein concentration

Apolipophorin III (apoLp-III) plays a key role in lipid mobilization during prolonged flight of the migratory locust, Locusta migratoria. In larval animals, only small amounts of hemolymph apoLp-III are present, while after adult emergence its concentration increases rapidly. In this study the maximum apoLp-III concentration was found in 19-day-old adult locusts: 17 mg/ml. After reaching this level, the apoLp-III concentration then decreased to 6 mg/ml. Determination of apoLp-III mRNA levels in fat body tissue revealed a similar pattern for apoLp-III gene expression. The possible role of juvenile hormone (JH) in controlling apoLp-III synthesis was studied using precocene which prevents JH synthesis, and methoprene, a stable JH analog. Blocking of JH synthesis by inactivation of the corpora allata with precocene resulted in a slow gradual increase in the hemolymph apoLp-III concentration: A maximum level of 18 mg/ml was now obtained after 5 weeks. Furthermore, a subsequent decrease in apoLp-III levels did not occur in older animals. Treatment of locusts with methoprene resulted in a reduction of both hemolymph apoLp-III as well as fat body mRNA levels compared to control animals. Administration of both methoprene and precocene to adult locusts resulted in a 60% reduction of the apoLp-III concentration compared to precocene treated animals. The above results suggest that expression of apoLp-III is not only up-regulated shortly after adult emergence but also down-regulated by factors in which JH might be involved.