Trehalase polymorphism in Drosophila melanogaster

Physiological roles of trehalose in Leptinotarsa larvae revealed by RNA interference of trehalose-6-phosphate synthase and trehalase genes

Trehalose is proposed to serve multiple physiological roles in insects. However, its importance remains largely unconfirmed. In the present paper, we knocked down either a trehalose biosynthesis gene (trehalose-6-phosphate synthase, LdTPS) or each of three degradation genes (soluble trehalases LdTRE1a, LdTRE1b or membrane-bound LdTRE2) in Leptinotarsa decemlineata by RNA interference (RNAi). Knockdown of LdTPS decreased trehalose content and caused larval and pupal lethality. The LdTPS RNAi survivors consumed a greater amount of foliage, obtained a heavier body mass, accumulated more glycogen, lipid and proline, and had a smaller amount of chitin compared with the controls. Ingestion of trehalose but not glucose rescued the food consumption increase and larval mass rise, increased survivorship, and recovered glycogen, lipid and chitin to the normal levels. In contrast, silencing of LdTRE1a increased trehalose content and resulted in larval and pupal lethality. The surviving LdTRE1a RNAi hypomorphs fed a smaller quantity of food, had a lighter body weight, depleted lipid and several glucogenic amino acids, and contained a smaller amount of chitin. Neither trehalose nor glucose ingestion rescued these LdTRE1a RNAi defects. Silencing of LdTRE1b caused little effects. Knockdown of LdTRE2 caused larval death, increased trehalose contents in several tissues and diminished glycogen in the brain-corpora cardiaca-corpora allata complex (BCC). Feeding glucose but not trehalose partially rescued the high mortality rate and recovered glycogen content in the BCC. It seems that trehalose is involved in feeding regulation, sugar absorption, brain energy supply and chitin biosynthesis in L. decemlineata larvae.

Trehalase regulates neuroepithelial stem cell maintenance and differentiation in the Drosophila optic lobe

As one of the major hydrolases in Drosophila, trehalase (Treh) catalyzes the hydrolysis of trehalose into glucose providing energy for flight muscle activity. Treh is highly conserved from bacteria to humans, but little is known about its function during animal development. Here, we analyze the function of Treh in Drosophila optic lobe development. In the optic lobe, neuroepithelial cells (NEs) first divide symmetrically to expand the stem cell pool and then differentiate into neuroblasts, which divide asymmetrically to generate medulla neurons. We find that the knockdown of Treh leads to a loss of the lamina and a smaller medulla. Analyses of Treh RNAi-expressing clones and loss-of-function mutants indicate that the lamina and medulla phenotypes result from neuroepithelial disintegration and premature differentiation into medulla neuroblasts. Although the principal role of Treh is to generate glucose, the Treh loss-of-function phenotype cannot be rescued by exogenous glucose. Thus, our results indicate that in addition to being a hydrolase, Treh plays a role in neuroepithelial stem cell maintenance and differentiation during Drosophila optic lobe development.

AGI, a previously unreported D. melanogaster alpha-glucosidase: partial purification, characterization, and cytogenetic mapping

Inbred Drosophila melanogaster stocks were surveyed for alpha-glucosidases with nondenaturing gel electrophoresis using a fluorogenic substrate to stain the gels. The glucosidase most active under these conditions is polymorphic. We established that the polymorphism is genetic in origin and that the glucosidase was not likely to be a previously characterized enzyme. The gene encoding the enzyme was mapped cytogenetically to 33 A1-2- 33A8-B1, confirming that this is an enzyme not yet reported in D. melanogaster. The enzyme was partially purified by elution from nondenaturing gels, which enabled us to establish that it has optimal activity at pH 6 and interacts most strongly with alpha-1-4 glucosides. A developmental and tissue survey suggested that this enzyme could have a purely digestive role or be involved in carbohydrate metabolism inside the organism. We propose that this enzyme is involved in either starch digestion or glycogen metabolism.

Rapid enzyme kinetic assays of individual Drosophila and comparisons of field-caught D. melanogaster and D. simulans

Techniques for performing numerous enzyme kinetic assays with minimum time and effort would be valuable to studies of the evolutionary genetics of metabolic control and the quantitative genetics of determinants of kinetic parameters. Microtiter plate readers have been used for a variety of repetitious analytical techniques, and instruments are available that can take repetitive readings with sufficient speed to perform kinetic assays. The ability of these instruments to assay rapidly the kinetic properties of small samples makes them potentially useful for a number of problems in population genetics. While the ability to handle large numbers of samples is very attractive, the small sample volumes and optical imprecision of microtiter plates result in some sacrifice in accuracy. This paper presents methods for performing kinetic assays on individual field-caught Drosophila, quantifies the precision of these methods, and characterizes differences among Drosophila melanogaster and D. simulans from samples caught in California and Pennsylvania. Comparisons between field-caught and laboratory reared D. melanogaster show that most of the characters are very similar, with the exception of alpha GPDH, which has a threefold higher mean activity among field-caught flies. The phenotypic correlations are presented with a brief discussion of their relevance to assessing the evolution of metabolic control of these enzymes.