Fourth International Symposium on Molecular Insect Science

Plasmodium, the causative agent of malaria, has to complete a complex developmental program in its mosquito host for transmission to occur. However, little is known at the molecular level about mosquito-parasite interactions. By use of subtraction libraries, we have begun an analysis of mosquito and parasite genes expressed during Plasmodium berghei development in Anopheles stephensi. The libraries were obtained by subtracting mRNA of noninfected blood-fed mosquito guts and/or Plasmodium asexual stages from mRNA of P. berghei ookinetes or infected mosquito guts. Libraries enriched for genes preferentially expressed at 4 developmental stages were prepared: 1) in vitro cultured ookinetes, 2) early oocysts, 3) middle oocysts, and 4) late oocysts. A total of 1,657 unique sequences were identified among the 2182 clones that were sequenced. Of these, 1032 were of presumptive mosquito origin (<55% AT) and 625 of Plasmodium origin (>55% AT). Northern blot analysis of several randomly selected genes indicates upregulation at a time of development corresponding to the library of origin. A polyclonal antibody to a putative cell surface ookinete protein containing a von Willebrand type A adhesive domain inhibited oocyst formation by 60-79%, making this a candidate for transmission-blocking antigen. Clones encoding three different mosquito caspases were isolated. Interestingly, the three genes are induced in the midgut epithelium at the time of parasite invasion.