1)As in the silkworm Bombyx mori and the fruitfly Drosophila melanogaster, we have identified the same serine proteinase casecade (Prophenoloxidase cascade) responsible for the synthesis of melanin after an injury or during microbial invasion. However, in Anopheles gambia, the major vector of malaria parasites, this cascade is indeed present but with regard to Plasmodium falciparum does not get triggered during invasion of ookinetes or sporozoites.
To better understand how the cascade operates in the mosquito Anopheles gambiae we have used Drosophila as a model system. We have isolated and recently characterized a novel serpin, naturally occuring serine proteinase inhibitor, that regulates the activation of the prophenoloxidase cascade. Furthermore, we have demonstrated that this serpine is involved in blood (hemolymph) coaggulation. Hence, this serpin is involved in the regulation of two distinct physiological processes: melanization and blood coaggulation, both of which are very important in insect defense. At present, we are searching for a serpin homolog in Anopheles gambiae as well as in Plasmodium in order to see if it could be involved in the inhibition of melanization during Plasmodium infections in the mosquito.
2) Plasmodium fertility and fertilisation (Richard Paul, Anna Raibaud and Paul Brey)
At present we are studying sex determination and fertilisation in Plasmodium, the etiological agent of malaria, using notably the avian malaria model Plasmodium gallinaceum. The study of the role of kinase pathways in the sexual differentiation process will enable us to identify novel targets for anti-malarial drugs. Additionally, following the isolation of new strain of the second species of avian malaria, P. juxtanucleare, we have been able to demonstrate the occurrence of interspecific interactions at the moment of parasite fertilisation in the mosquito. Such experimental evidence coupled with the near identical sequences of conserved genes strongly suggests the potential for species hybridisation.
3) Genomics of Anopheles gambiae (Charles Roth, Marine Grailles and Paul Brey)
For several years our unit has been working on the genome of the mosquito vector Anopheles gambiae. The sequence database GenBank contains about 24,000 A. gambiae sequences of which 17,500 are the insert ends of a Bacterial Artificial Chromosome (BAC) library that was partially sequenced by Genoscope and annotated in our laboratory.
Anopheles gambiae has the second most sequenced insect genome after only that of Drosophila melanogaster and our objective is to carry out a detailed comparison of the genomic sequences of these two organisms. Currently, four BAC clones from a particularly interestingregion on chromosome 2 of A. gambiae have been completely sequenced and a number of genes have been identified that are orthologs of genes located on the right arm of chromosome 3 in Drosophila. In order to study the synteny of the genes on the chromosomes of these two insects, we have been working in collaboration with F. H. Collins (Univ. of Notre Dame, U.S.A.) to identify the location of the gene sequences we have identified in the BAC end sequences and to compare the location to those of their Drosophila counterparts. The preliminary results indicate that orthologous genes in the two organisms are very highly related and that in some cases neighboring genes remain together in the two organisms. It will be interesting and important to know if synteny has been maintained for functional reasons during the 50 million years of evolution since the two
dipteran insects shared a common ancestor. An understanding of why certain genes have maintained a close physical proximity on the chromosomes while others have been displaced to other environments will be important if we are to transfer the the abundant information generated about the most studied higher eukaryote, the fruit fly, to the vectors that can constitute a great danger to public health.