Environmental Engineering Reference
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with RT-PCR were often higher. The underestimation of transcription ratios obtained
from microarray data is likely due to technical issues and has been previously evi-
denced in other studies [14, 42].
Over-transcription of genes encoding P450s has been frequently associated with
metabolic-based insecticide resistance mechanisms in insects [10]. In mosquitoes, the
CYP6Z
subfamily has been previously associated with response to pyrethroid, carba-
mates, and organochlorine insecticides. In
Ae. aegypti
,
CYP6Z9
has been found 4-fold
over-transcribed in a permethrin-resistant strain collected in Northern Thailand [20].
In two recent studies,
CYP6Z8
was also identifi ed as inducible by permethrin and other
pollutants [14, 15]. In
An. gambiae
,
CYP6Zs
have been frequently found constitutively
over-transcribed in permethrin- and DDT-resistant strains [19, 21, 43]. Recent studies
demonstrated that the enzyme encoded by
An. gambiae CYP6Z1
can metabolize the
insecticides carbaryl and DDT while
CYP6Z2
with a narrower active site, can only
metabolize carbaryl [44, 45]. Recently, another
An. gambiae
P450 (
CYP6P3
), was
shown to be able to degrade pyrethroid insecticides [22]. The over-transcription of
CYP6Z6
in the Vauclin strain may indicate the involvement of
Ae. aegypti
CYP6Zs
in insecticide resistance in Martinique. However, the decisive demonstration of their
capability to metabolize insecticides requires further investigations.
The association of
CYP6Ms
with metabolic resistance to pyrethroids has also been
previously described in mosquitoes. In
Ae. aegypti
larvae,
CYP6M6
and
CYP6M11
were found inducible by permethrin and pollutants [14]. Although no
Aedes CYP6Ms
have been found constitutively over-transcribed in other insecticide-resistant strains,
An. gambiae
CYP6M2
was found signifi cantly over-transcribed in various strains re-
sistant to pyrethroids [21, 46]. Recent studies indicate that
CYP6M2
is able to me-
tabolize pyrethroid insecticides (Stevenson B. personal communication). Our results
suggest that
Ae. aegypti
CYP6M6
and
CYP6M11
, with protein sequences similar to
An.
gambiae
CYP6M2
, might also be involved in resistance of
Ae. aegypti
to pyrethroids
in Martinique.
Finally, the glutathione S-transferase
GSTE7
and the carboxy/cholinesterase
CCE-
ae3A
were both found over-transcribed in both life-stages of the Vauclin strain. The
role GSTs in resistance to chemical insecticides has been previously evidenced in in-
sects with the enzyme encoded by
An. gambiae GSTE2
metabolizing DDT [35, 47, 48]
and the housefl y
MdGST6-A
metabolizing two organophosphate insecticides [49]. In
Ae. aegypti, GSTE2
also metabolises DDT and is over-transcribed in a pyrethroid and
DDT-resistant strain from Thailand [35]. In 2008, Strode et al. [20] also revealed the
over-transcription of
GSTE7
in pyrethroid-resistant mosquitoes. Our results confi rm
that
GSTE7
might have a role in insecticide resistance in
Ae. aegypti.
Over-production
of carboxylesterases has been showed to play an important role in resistance to or-
ganophosphate insecticides in mosquitoes [50-53]. Elevated esterase activities confer-
ring resistance to organophosphate insecticides has usually been linked to genomic
amplifi cation of specifi c alleles although gene over-transcription may also be involved
[12]. Considering the high resistance of larvae of the Vauclin strain to temephos, over-
transcribed CCEs represent good candidates for organophosphate metabolism in
Ae.
aegypti
.
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