Comparative analysis of BAC and whole genome shotgun sequences from an Anopheles gambiae region related to Plasmodium encapsulation

Abstract

The only natural mechanism of malaria transmission in sub-Saharan Africa is the mosquito, generally Anopheles gambiae. Blocking malaria parasite transmission by stopping the development of Plasmodium in the insect vector would provide a useful alternative to the current methods of malaria control. Toward this end, it is important to understand the molecular basis of the malaria parasite refractory phenotype in An. gambiae mosquito strains. We have selected and sequenced six bacterial artificial chromosome (BAC) clones from the Pen-1 region that is the major quantitative trait locus involved in Plasmodium encapsulation. The sequence and the annotation of five overlapping BAC clones plus one adjacent, but not contiguous clone, totaling 585kb of genomic sequence from the centromeric end of the Pen-1 region of the PEST strain were compared to that of the genome sequence of the same strain produced by the whole genome shotgun technique. This project identified 23 putative mosquito genes plus putative copies of the retrotransposable elements BEL12 and TRANSIBN1_AG in the six BAC clones. Nineteen of the predicted genes are most similar to their Drosophila melanogaster homologs while one is more closely related to vertebrate genes. Comparison of these new BAC sequences plus previously published BAC sequences to the cognate region of the assembled genome sequence identified three retrotransposons present in one sequence version but not the other. One of these elements, Indy, has not been previously described. These observations provide evidence for the recent active transposition of these elements and demonstrate the plasticity of the Anopheles genome. The BAC sequences strongly support the public whole genome shotgun assembly and automatic annotation while also demonstrating the benefit of complementary genome sequences and of human curation. Importantly, the data demonstrate the differences in the genome sequence of an individual mosquito compared to that of a hypothetical, average genome sequence generated by whole genome shotgun assembly.