Normal and experimentally induced lysosomal activity in the larval fat body of Calliphora erythrocephala Meigen

The Insect Hemolymph Protein HP19 Mediates the Nongenomic Effect of Ecdysteroids on Acid Phosphatase Activity

The activity of acid phosphatase (ACP) in insect fat bodies is stimulated by the steroid hormone 20-hydoxyecdysone (20E) in vivo. However, in fat bodies kept in culture, a factor from the hemolymph is required to enhance the ACP activity. We identified the factor as a protein with a molecular mass of 19 kDa (HP19) from the hemolymph of a lepidopteran insect, the rice moth, Corcyra cephalonica. Western analysis of hemolymph proteins with denaturing and non-denaturing PAGE using antibodies raised against HP19 suggest that this protein exists as a monomer. It is synthesized by the hind gut-associated lobular fat body of the larvae and is released into the hemolymph. The stimulatory effect of HP19 on the ACP activity is developmentally regulated and exhibits its maximal effect shortly before the onset of metamorphosis. We cloned the HP19 cDNA by immunoscreening a hind gut-associated lobular fat body cDNA expression library. Analysis of the amino acid sequence shows that HP19 belongs to the family of glutathione S-transferase (GST) like proteins. However, affinity-purified GST from Corcyra failed to show any mediation effect on 20E-stimulated ACP activity, and HP19 lacks GST enzymatic activity. Notably, HP19 mediates the hormone-stimulated ACP activity in intact fat body tissue and homogenates even in the presence of inhibitors of transcription and translation, suggesting a nongenomic mode of action. In addition, we show that HP19 inhibits the 20E-induced phosphorylation of the hexamerin receptor protein.

Cyclic AMP in the fat body of Mamestra brassicae during the last instar and its possible involvement in the cellular autophagocytosis induced by 20-Hydroxyecdysone

The amount of cAMP was assayed by a competitive protein binding method in fat body cells of Mamestra brassicae, during the last larval stage and after administration of 20-hydroxyecdysone. When expressed as picomoles of cAMP per milligram fresh weight of tissue, two increases in its concentration were observed on the 3rd and on the 6th days. However, only the first peak appeared on the curve when cAMP concentration was expressed as picomoles cAMP per milligram of protein of tissue homogenate. Electron microscopical examination of the tissue showed that the first increase of cAMP level coincided with the beginning of the formation of autophagic vacuoles and revealed a heavy accumulation of protein storage granules in the cells, starting on the 4th day. This process might mask the second rise of cAMP level when tissue protein content is taken as the basis for calculation. 20-Hydroxyecdysone (5 micrograms/g body wt) administered to 48-hr-old larvae induced premature autophagocytosis in the fat body cells and a sharp rise in their cAMP content, reaching within 3 hr a level as high as observed in the 3-day-old untreated larvae. Autophagy was also enhanced in the cells exposed to dibutyryl cAMP or theophylline either in vivo or in vitro. Based on these data we think that cAMP content of the fat body is controlled by ecdysone and that cAMP plays a significant role in the regulation of autophagocytosis in this tissue during metamorphosis.

X-ray micronalysis of copper and sulphur-containing granules in the fat body cells of homopteran insects

Regions of the fat body of larvae of Chaetophyes compacta and Pectinariophyes sp. (Machaerotidae, Homoptera) which are closely associated with mycetomes have been analysed by electron probe X-ray microanalysis. It is shown that cells in these regions contain electron probe X-ray microanalysis. It is shown that cells in these regions contain electron dense granules which are rich in copper and sulphur. These two elements occur in the atomic ratio of 3:2 respectively. It is conjectured that copper may be bound to a sulphur containing metallothionein and that the granules represent either the end products of copper detoxification or serve as copper stores for synthesis of enzymes and macromolecules by the mycetomal symbionts.