Plasmodium genes responsible for oocyst development and interaction with its Anopheline vector

Abstract

The transmission of the malaria parasite Plasmodium is governed by a complex developmental cycle. This PhD thesis describes the transcriptional profiling of the rodent malaria parasite Plasmodium berghei developmental migration through its A. gambiae vector. The study was conducted in vivo, using a near complete P. berghei genome microarray platform. Emphasis was placed on the oocyst stage, as little is known about the genes implicated in the ookinete to oocyst transition, and oocyst maturation. The data presented here provide novel transcriptional information about Plasmodium transmission. The analysis revealed a large shift in gene utilisation as the parasite makes its transition from the motile ookinete to the sessile oocyst. Furthermore, this work has shown that different sets of co-regulated genes are important for early and late oocyst development. In addition, this PhD thesis outlines the characterisation of a novel Plasmodium formin-like protein essential for rodent malaria transmission named the male inherited sporulation factor important for transmission (misfit). MISFIT is expressed in the early mosquito stages, where the protein localises to the parasite nucleus. Misfit exhibits an absolute requirement for paternal inheritance, which is in accordance with an observed male-biased expression pattern. pbmisfitΔ ookinetes display significant ultrastructural and gene expression defects and fail to complete zygotic meiosis. However, pbmisfitΔ ookinetes retain functionality and can successfully cross the midgut epithelial barrier. In contrast, mosquito infections with pbmisfitΔ resulted in an arrest immediately upon ookinete-oocyst transformation, where defective oocysts fail to sporulate. An essential role in chromosome segregation during mitosis / meiosis is postulated for MISFIT. In conclusion, the work presented in this thesis has established the ookinete-oocyst transition as a major cell cycle check point during malaria transmission and identified misfit as the first male inherited Plasmodium gene known to affect development post-fertilisation.