Drosophila as a model for the Anopheles Malpighian tubule

Overend, Gayle (2010) Drosophila as a model for the Anopheles Malpighian tubule. PhD thesis, University of Glasgow.

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Abstract

The insect Malpighian tubule is involved in osmoregulation, detoxification and
immune function, physiological processes which are essential for insect
development and survival. As the Malpighian tubules contain many ion channels
and transporters, they could be an effective tissue for targeting with novel
pesticides to control populations of Diptera. Many of the insecticide compounds
used to control insect pest species are no longer suited to their task, and so new
means of control must be found. The malarial mosquito, Anopheles gambiae,
spreads the Plasmodium parasite which is responsible for over one million deaths
each year, and is one of the species on which many current insecticides are no
longer effective. Anopheles is notoriously difficult to study due to a lack of
natural mutation stocks and transgenic capabilities, as well as the difficulties
involved with maintaining a colony. The fruit-fly Drosophila melanogaster is a
useful model organism for Anopheles, and previous studies suggest that the
mechanisms of Malpighian tubule function are well conserved between the two
species.
Following microarray investigations to identify genes which were highly enriched
in both the Anopheles and Drosophila Malpighian tubules, four homologous genepairs
were selected, AGAP097752 and CG15406, AGAP012251 and Picot,
AGAP009005 and ZnT35C, and AGAP002587 and CG8028. Analysis of the
Anopheles Malpighian tubule microarray data-set showed ion channels and
transporters to be highly expressed in the tubules, although similarly to
Drosophila, very few of the renal up-regulated genes have been characterised.
The gene-pairs chosen were all novel, but putatively predicted to be involved in
sugar transport, phosphate transport, zinc transport and monocarboxylate
transport respectively. These are functions which are likely to be essential, but
so far remain unstudied in the insect renal system. The gene-pairs were chosen
with two main purposes; to determine how closely expression of the genes was
conserved between Anopheles and Drosophila, and also to determine which of
the genes were essential, and could therefore be effective insecticide targets.
The homologous gene-pair AGAP007752 and CG15406 have well-conserved
expression in the Malpighian tubules, suggesting that they are functionally
important genes. This was shown in Drosophila, where knockdown of CG15406
4
expression was lethal to the fly. A direct role in tubule fluid secretion was not
found, and experiments to determine the sugars transported by CG15406 were
inconclusive, possibly due to an abundance of highly-expressed sugar
transporters in the tubules. The inorganic phosphate co-transporters
AGAP012251 and Picot also show conservation of expression in the Malpighian
tubules, and are likely to be involved in the transport of inorganic phosphate
into the tubules for incorporation into metallo-organic concretions. In the
Anopheles tubules the concretions are found in the main segment, in the
Drosophila tubules they are located in the distal initial and transitional
segments, where AGAP012251 and Picot are expressed. Picot is essential for
Drosophila development through to adulthood, and for survival as an adult,
although the transporter does not appear to be directly involved in fluid
secretion. Expression of neither AGAP012251 nor Picot is confined to the
tubules. The putative zinc transporters AGAP009005 and ZnT35C show a highly
conserved expression pattern, and appear to be involved in the secretion of
excess zinc from the Malpighian tubules. ZnT35C is essential early-on in
Drosophila development, and for survival in the adult fly. Similarly to Picot and
CG15406, there is no direct role for ZnT35C in fluid secretion from the tubules
under normal zinc conditions. The putative monocarboxylate transporters
AGAP002587 and CG8028 are not as well conserved, as AGAP002587 is highly upregulated
in the tubules of female mosquitoes both before and after a bloodfeed,
whereas CG8028 has no sex-specific up-regulation. CG8028 is not essential
for Drosophila development or survival, and plays no discernable role in fluid
secretion.
The data collected during this investigation suggests that in general there is a
high level of conservation of expression between homologous transport genes in
the Anopheles and Drosophila Malpighian tubules. The three gene-pairs which
show the greatest conservation of expression are also essential for development
and survival in Drosophila. This suggests that cross-species studies are an
effective way of finding essential and important genes. The data collected also
suggests that Drosophila is a reliable model for Anopheles, and could be used as
a high-throughput system of finding genes which could be effective insecticide
targets in Diptera.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Anopheles, Drosophila, insect renal physiology, model organisms, insecticide resistance
Subjects: Q Science > QH Natural history > QH301 Biology
Q Science > QH Natural history > QH426 Genetics
Colleges/Schools: College of Medical Veterinary and Life Sciences > Institute of Neuroscience and Psychology
Supervisor's Name: Dow, Prof. Julian A.T.
Date of Award: 2010
Depositing User: Miss Gayle Overend
Unique ID: glathesis:2010-1604
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 07 Dec 2010
Last Modified: 10 Dec 2012 13:43
URI: http://theses.gla.ac.uk/id/eprint/1604

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