Interactions between detoxification mechanisms and excretion in Malpighian tubules ofDrosophila melanogaster

Abstract

SUMMARY Insects have long been known to excrete toxins via the Malpighian (renal) tubules. In addition, exposure to natural or synthetic toxins is commonly associated with increases in the activity of detoxification enzymes such as the P450 monoxygenases (P450s) and the glutathione-S-transferases (GSTs). We examined the links between mechanisms for detoxification and excretion in adult Drosophila melanogaster using functional assays and measurements of changes in gene expression by quantitative reverse transcriptase PCR in response to dietary exposure to compounds known to alter activity or gene expression of P450s and GSTs. Dietary exposure to phenol, which alters gene expression for multiple GSTs after seven to 10 generations, was also associated with an increase (more than twofold) in secretion of the organic anion methotrexate (MTX) by isolated tubules. Dietary exposure to the insecticide synergist piperonyl butoxide (PBO) was associated with reduced expression of two P450 genes (Cyp4e2, Cyp4p1) and two GST genes (GstD1, GstD5) in the tubules, as well as increased expression of Cyp12d1 and GstE1. Thin layer chromatographic analysis of fluid secreted by isolated tubules indicated that dietary exposure to PBO resulted in increased levels of an MTX metabolite. In addition, exposure to PBO altered the expression of transporter genes in the tubules, including a Drosophila multidrug resistance-associated protein, and was associated with a 73% increase in MTX secretion by isolated tubules. The results suggest that exposure of Drosophila to toxins evokes a coordinated response by the Malpighian tubules, involving both alterations in detoxification pathways as well as enhanced transport.

Selection and Validation of Reference Genes for Functional Studies in the Calliphoridae Family

“…GstD1 encodes a glutathione-Stransferase involved in detoxification metabolism. This gene is regulated when an insect is exposed to a variety of organic compounds (Chahine and O'Donnell 2011). The compared species have different feeding preferences and were fed in different media.…”

Glutathione-S-transferase profiles in the emerald ash borer, Agrilus planipennis

“…ApGST-E2 was also high in Malpighian tubules, an important physiological (renal) tissue that is vital in eliminating dietary toxins as reported in other insects (Chahine and O'Donnell, 2011). A recent study in D. melanogaster suggested that exposure to toxins evoked a coordinated response by the Malpighian tubules, involving the interaction of detoxification pathways (including GSTs) as well as enhanced excretion (Chahine and O'Donnell, 2011). On the other hand, ApGST-E2 was highly expressed in fat body which is also an important metabolic tissue for detoxification as demonstrated earlier in A. planipennis (Mittapalli et al, 2010) and in the Hessian fly, Mayetiola destructor (Mittapalli et al, 2007).…”

“…Several studies of plant-insect interaction have shown the midgut tissue as the major interface for several detoxification enzymes including GSTs (Hakim et al, 2010;Mittapalli et al, 2010;Pauchet et al, 2010;Rajarapu et al, 2011;Zhang et al, 2012). ApGST-E2 was also high in Malpighian tubules, an important physiological (renal) tissue that is vital in eliminating dietary toxins as reported in other insects (Chahine and O'Donnell, 2011). A recent study in D. melanogaster suggested that exposure to toxins evoked a coordinated response by the Malpighian tubules, involving the interaction of detoxification pathways (including GSTs) as well as enhanced excretion (Chahine and O'Donnell, 2011).…”

“…Abundant mRNA levels of this gene in vital tissues including midgut, and Malpighian tubules might be due to high stress levels encountered by these tissues during the metabolism of ash toxins and/or the result of other physiological processes. Recent reports demonstrated that Malpighian tubules are also known to play a role in detoxification of xenobiotics (Dow, 2009;Beyenbach et al, 2010;Chahine and O'Donnell, 2011). Transcript levels of ApGST-O1 were high in midgut and Malpighian tubules.…”

Identification of immunological expressed sequence tags in the mealworm beetle Tenebrio molitor

“…In Tenebrio we found expression of cytochrome p450, known for a role in detoxification post-infection (Chahine, 2011;Chung et al, 2011). One sequence in particular, aligned with stress-induced phosphoprotein 1, showed ontologies with various aspects of stress management, development and immune function.…”