The early parasite development in the mosquito is mostly driven by previously synthesised transcripts in the gametocyte. However, the role of gametocyte players in later sporogonic stages in the vector is relatively unknown. The in vivo transcriptional profiling of P. berghei during the first hour in the Anopheles gambiae midgut was employed in combination with published proteome data, to identify Plasmodium gametocyte enriched genes with functions in downstream sporogonic development. Additionally, differentially regulated Plasmodium genes were also selected from a transcriptional profiling of P. falciparum during the first 24 hours of development in Anopheles gambiae and Anopheles arabiensis. This led to the identification of six genes that are essential for malaria transmission. PBANKA_1353800 and PBANKA_0720900, identified from the P. berghei array are essential for ookinete motility and oocyst sporogony respectively. P. falciparum orthologous PBANKA_0201700, PBANKA_1422900, PBANKA_1457700 and PBANKA_1119200, identified from the P. falciparum array are essential for the ookinete to oocyst transition.
Functional characterization was also undertaken for the subtilisin-like domain in SUBO, a protein previously shown to be important for midgut invasion. This revealed that while this domain lacks residues important for catalytic activity, this domain is necessary for the invasion function of SUBO.
Finally, this thesis presents the identification of a novel gene regulation during Plasmodium development in the mosquito. By utilizing various transgenic reporters in in vivo and in vitro fertilization experiments, the paternal genome is shown to be transcriptionally silent during ookinete development.
These data contribute to the knowledge of the Plasmodium genes responsible for the gametocyte to ookinete to oocyst developmental transitions, and the functional parental origin of these genes during development in the mosquito. These essential genes are targets for the development of transmission blocking interventions.