Abstract:
Background:
Anopheles gambiae,
one of the main Afro-tropical mosquito vector of malaria, has adapted to heavy
metals in its natural habitat, and developed resistance to most conventional insecticides. Investigations were
conducted to establish an association between tolerance to cadmium or lead-heavy metals, and expression of
specific genes for cytochrome p450 enzymes associated with pyrethroid resistance in the mosquito.
Methods:
Juvenile aquatic stages of the mosquito were selected for tolerance to cadmiun or lead through chronic
exposure of the stages to maximum acceptable toxicant concentrations (MATCs) of the metals. Using real-time
quantitative polymerase chain reaction (qPCR), three replicates each of male or female cadmium or lead-tolerant
individuals and relevant controls were separately screened for expression of
CYP6M2
,
CYP6P3
and
CYP6Z1
genes.
The variance in expression levels of the genes amongst the treatments was compared by ANOVA statistical tool.
Results:
Expressions of all the genes were significantly lower (P <0.05) in females than in males. Within gender,
there 1.3 - 2.3 or 3.1-4.2-fold reduction in expression of the genes in cadmium or lead selected than respective
control populations. Expression of all the classes of gene was elevated in cadmium selected female populations
relative to their respective controls.
Conclusion:
These findings suggest that tolerance to cadmium or lead in the mosquito can influence response in
cytochrome p450 genes associated with metabolism of pyrethroids in the mosquito in a sex-specific manner. This
can, in turn, affect sensitivity of the mosquito to pyrethroids and other xenobiotics associated with these genes,
with potential implications in mosquito vector control operations.