Abstract:
The variation of the mannose-binding protein (MBP) gene and the role of lectins during infection in mosquitoes were investigated using genomic DNA approach based on sequencing of the gene and the levels of its expression determined using semi-quantitative Reverse Transcriptase Polymerase Chain Reaction (RT-PCR) approach. Using shotgun cloning ~trategy, sequences were determined from cloned PCR products obtained from genomic DNA of An.gambiae, s.s, An. arabiensis and An. funestus and aligned following amino acid translation. BLAST program revealed that MBP-M 1, MBP-13 and MBP 15 clones showed high homology, with Anopheles protein precusor A 16 (Accession 093118). These results were further confirmed by pairwise alignment using CLUSTAL W program. The remaining clones ( MBP-M2, MBP-MW1, MBP-MW4, MBP-MW5, MBP-MW12, MBP-C1 AND MBP-C1 5) showed no signature of C-type lectin domain but were closely related based on the positioning of these genes on the polytene chromosome. Phylogenetic analysis indicated that MBP-M 1, MBP-13 and MBP-15 clones are closely related. Since the representatives of the MBP clones harbour comparatively short fragments, clustering of these clones on the nodes supports a more close phylogenetic relationship between and within Anopheles sp. RT-PCR analysis showed that MBP is expressed differently with respect to blood-meal status of the mosquitoes. Altered expression of MBP may contribute to the risk of disease transmission by the Plasmodium. The studies also showed that MBP levels decreased with time post-infection. These changes may disturb normal MBP levels and create favourable condition for parasite establishment within the mosquito midgut. These observations raise the possibility that low levels of MBP may contribute to the increased malaria transmission by the mosquito and hence Plasmodium plays a key role in its down-regulation.