Drosophila as a model for the Anopheles Malpighian tubule

QH301 Biology;QH426 Genetics

Overend, Gayle ; Dow, Julian A.T.

University:University of Glasgow

Department:Institute of Neuroscience and Psychology

关键词: Anopheles, Drosophila, insect renal physiology, model organisms, insecticide resistance;   

Others  :  http://theses.gla.ac.uk/1604/1/2009overendphd.pdf

来源: University of Glasgow

【 摘 要 】

The insect Malpighian tubule is involved in osmoregulation, detoxification andimmune function, physiological processes which are essential for insectdevelopment and survival. As the Malpighian tubules contain many ion channelsand transporters, they could be an effective tissue for targeting with novelpesticides to control populations of Diptera. Many of the insecticide compoundsused to control insect pest species are no longer suited to their task, and so newmeans of control must be found. The malarial mosquito, Anopheles gambiae,spreads the Plasmodium parasite which is responsible for over one million deathseach year, and is one of the species on which many current insecticides are nolonger effective. Anopheles is notoriously difficult to study due to a lack ofnatural mutation stocks and transgenic capabilities, as well as the difficultiesinvolved with maintaining a colony. The fruit-fly Drosophila melanogaster is auseful model organism for Anopheles, and previous studies suggest that themechanisms of Malpighian tubule function are well conserved between the twospecies.Following microarray investigations to identify genes which were highly enrichedin both the Anopheles and Drosophila Malpighian tubules, four homologous genepairswere selected, AGAP097752 and CG15406, AGAP012251 and Picot,AGAP009005 and ZnT35C, and AGAP002587 and CG8028. Analysis of theAnopheles Malpighian tubule microarray data-set showed ion channels andtransporters to be highly expressed in the tubules, although similarly toDrosophila, very few of the renal up-regulated genes have been characterised.The gene-pairs chosen were all novel, but putatively predicted to be involved insugar transport, phosphate transport, zinc transport and monocarboxylatetransport respectively. These are functions which are likely to be essential, butso far remain unstudied in the insect renal system. The gene-pairs were chosenwith two main purposes; to determine how closely expression of the genes wasconserved between Anopheles and Drosophila, and also to determine which ofthe genes were essential, and could therefore be effective insecticide targets.The homologous gene-pair AGAP007752 and CG15406 have well-conservedexpression in the Malpighian tubules, suggesting that they are functionallyimportant genes. This was shown in Drosophila, where knockdown of CG154064expression was lethal to the fly. A direct role in tubule fluid secretion was notfound, and experiments to determine the sugars transported by CG15406 wereinconclusive, possibly due to an abundance of highly-expressed sugartransporters in the tubules. The inorganic phosphate co-transportersAGAP012251 and Picot also show conservation of expression in the Malpighiantubules, and are likely to be involved in the transport of inorganic phosphateinto the tubules for incorporation into metallo-organic concretions. In theAnopheles tubules the concretions are found in the main segment, in theDrosophila tubules they are located in the distal initial and transitionalsegments, where AGAP012251 and Picot are expressed. Picot is essential forDrosophila development through to adulthood, and for survival as an adult,although the transporter does not appear to be directly involved in fluidsecretion. Expression of neither AGAP012251 nor Picot is confined to thetubules. The putative zinc transporters AGAP009005 and ZnT35C show a highlyconserved expression pattern, and appear to be involved in the secretion ofexcess zinc from the Malpighian tubules. ZnT35C is essential early-on inDrosophila development, and for survival in the adult fly. Similarly to Picot andCG15406, there is no direct role for ZnT35C in fluid secretion from the tubulesunder normal zinc conditions. The putative monocarboxylate transportersAGAP002587 and CG8028 are not as well conserved, as AGAP002587 is highly upregulatedin the tubules of female mosquitoes both before and after a bloodfeed,whereas CG8028 has no sex-specific up-regulation. CG8028 is not essentialfor Drosophila development or survival, and plays no discernable role in fluidsecretion.The data collected during this investigation suggests that in general there is ahigh level of conservation of expression between homologous transport genes inthe Anopheles and Drosophila Malpighian tubules. The three gene-pairs whichshow the greatest conservation of expression are also essential for developmentand survival in Drosophila. This suggests that cross-species studies are aneffective way of finding essential and important genes. The data collected alsosuggests that Drosophila is a reliable model for Anopheles, and could be used asa high-throughput system of finding genes which could be effective insecticidetargets in Diptera.