Browsing by Author "Nyambaka, Hudson"

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Differential induction of proteins in Anopheles gambiae sensu stricto (Diptera: Culicidae) larvae in response to heavy metal selection
(2006) Mireji, Paul O; Keating, Joseph; Kenya, Eucharia; Mbogo, Charles; Nyambaka, Hudson; Osir, Ellie; Githure, John; Beier, John
Investigations were conducted to establish the magnitude and pattern of differential expression of proteins due to generational selection of third instar Anopheles gambiae s.s. Giles larvae by cadmium, copper and lead heavy metals, the three possible common urban pollutants. A susceptible strain of A. gambiae s.s. third instar larvae was separately placed under selection pressure with cadmium, copper and lead at LC30 and controls through five generations. First, third and fifth generation selection survivors were screened for differentially expressed proteins relative to non-exposed control by two-dimensional gel electrophoresis. Distribution patterns of the spots were analyzed by χ2 or Fishers' exact test and variations in expressions between and within generations by ANOVA. Most differentially expressed spots were acidic and of low molecular weight among all metals and generations. Type of heavy metal and generation were the main indicators of variations in differential expressions. Variation between generations was most significant among cadmium-selected populations of which the most number of spots were induced in the fifth generation. Most spots were induced in the copper-selected population in the third generation. The induced protein spots may be the products from respective genes that respond to heavy metals and counter their toxicity, thus building A. gambiae s.s. tolerance to these pollutants. The differential pattern and magnitude of expressed spots have potential application as molecular markers for assessment of anopheline adaptation status to heavy metals, and provide insight into the extent of environmental pollution
Expression of metallothionein and α-tubulin in heavy metal-tolerant Anopheles gambiae sensu stricto (Diptera: Culicidae)
(2010) Mireji, Paul O; Keating, Joseph; Hassanali, Ahmed; Impoinvil, Daniel E; Mbogo, Charles M; Muturi, Martha N; Nyambaka, Hudson; Kenya, Eucharia U; Githure, John I; Beier, John C
Anopheles mosquitoes have been shown to adapt to heavy metals in their natural habitats. In this study we explored the possibility of using Anopheles gambiae sensu stricto as bio-reporters for environmental heavy metal pollution through expressions of their metal-responsive metallothionein and α-tubulin genes. The study was undertaken with third instar larvae after selection by cadmium, copper, or lead at LC30 through five successive generations. Expression levels were determined in the 5th generation by semi-quantitative RT-PCR on the experimental and control populations. The data were analyzed using one-way ANOVA. The highest metallothionein (F3, 11=4.574, P=0.038) and α-tubulin (F3, 11=12.961, P=0.002) responses were observed in cadmium-tolerant treatments. There was significantly higher expression of metallothionein in cadmium or copper treatments relative to the control (P=0.012), and in cadmium than in lead treatments (P=0.044). Expressions of α-tubulin were significantly higher in cadmium than in control treatments (P=0.008). These results demonstrate the capacity of An. gambiae s.s. to develop tolerance to increased levels of heavy metal challenge. The results also confirm the potential of heavy metal-responsive genes in mosquitoes as possible bio-indicators of heavy metal environmental pollution. How the tolerance and expressions relate to An. gambiae s.s. fitness and vectorial capacity in the environment remains to be elucidated.
Heavy metals in mosquito larval habitats in urban Kisumu and Malindi, Kenya, and their impact
(2008) Mireji, PO; Keating, Joseph; Hassanali, Ahmed; Mbogo, Charles M; Nyambaka, Hudson; Kahindi, Samuel; Beierf, John C
Concentrations and distribution of cadmium, chromium, copper, iron, lead, manganese and zinc in mosquito larval habitats in urban Kisumu and Malindi, Kenya and their effect on the presence of Anopheles gambiae, Aedes aegypti, Culex quinquefasciatus and Anopheles funestus larvae were investigated. Manganese and iron were the most prevalent heavy metals in water of larval habitats in urban Kisumu and Malindi, respectively. Iron was the most prevalent heavy metal in bottom sediments in larval habitats in both cities. The highest concentrations of all heavy metals, except cadmium and iron, were recorded in the poorly planned–well drained stratum in the two cities. All heavy metals were more concentrated in human-made than in natural larval habitats. Copper was positively associated with the presence of Ae. aegypti, and lead was associated with the presence of An. gambiae and Ae. aegypti in urban Kisumu. Absence of significant correlation between the other metals and mosquito species in both cities, despite relatively high concentrations, suggest that the local larval populations, including key malaria vectors have adapted to the detected levels of these metals.