Malaria-Parasiten nutzen ein komplexes Repertoire aus Transportern, um sich durch ihren Lebenszyklus hindurch mit Nährstoffen aus Wirtszellen zu versorgen. Der Großteil der 144 Transporter von P. falciparum ist als essenziell für asexuelles Blutwachstum klassifiziert. Meine Hypothese war, dass ein Teil der bisher nicht untersuchten Transporter eine spezifische und essenzielle Rolle in den sexuellen Blutstadien von P. falciparum übernimmt und als Angriffspunkt dienen könnte, um die Transmission der Parasiten zu blockieren. Aus dem Transportom von P. falciparum wurden vielversprechende Gene identifiziert und durch experimentell-genetische Verfahren untersucht. Auf diesem Weg konnte ich einen Defekt bestätigen, der durch Fehlen von PfGEP1 hervorgerufen und bereits in der verwandten Spezies P. yoelii beschrieben wurde. Weder männliche noch weibliche Gametozyten konnten ohne GEP1 in der Lage Gameten bilden. Dies deutet auf eine zentrale Rolle für GEP1 in der Gametozyten-Aktivierung hin. Entsprechend groß ist das Potential, durch spezifische Inhibition von GEP1 die Übertragung von Malaria-Parasiten effizient zu unterbinden. Unterbrechung eines zweiten Gens namens MCP2 hatte keinen Effekt auf die Gametozyten von P. falciparum. Stattdessen wies P. berghei nach Fehlen von MCP2 einen Defekt bei der Sporozoitenbildung im Mitteldarm der Mücke auf. Nur in vereinzelten Oozysten konnten Sporozoiten gefunden werden und die Speicheldrüsen der infizierten Mücken enthielten kaum Sporozoiten. Somit hat die MCP2-Deletion keinen direkten Einfluss auf die Transmission vom Säugetierwirt auf die Mücke, jedoch erscheint MCP2 nötig für die Komplettierung des Lebenszyklus. Zusammenfassend bestätigen meine Daten die These, dass Transporterproteine in mindestens einem Stadium des Lebenszyklus von Plasmodium eine essenzielle Rolle spielen und liefern weitere Einblicke in die Funktion dieser Proteine. / During life cycle progression, Plasmodium parasites rely on a complex repertoire of transporter proteins to supply them with nutrients obtained from their host. Of the 144 transporter proteins annotated in Plasmodium falciparum, the majority has already been deemed likely essential for asexual blood growth. In this thesis, I hypothesized that a part of the unassigned parasitic transportome will be specifically essential to the sexual gametocyte stages and thus could contain transmission blocking targets for future application. The transportome of P. falciparum was screened in silico for potential candidates and the most promising genes were then targeted via a Crispr-Cas9-based disruption approach. Through this, I was able to confirm a defect in gametogenesis caused by disruption of PfGEP1 previously observed in P. yoelii. Both male and female gametocytes lacking GEP1 were unable to produce gametes. Overall, my data indicates that GEP1 plays a central role in the activation process, making it a promising transmission blocking target. Disruption of a second candidate gene called MCP2 did not affect P. falciparum asexual and sexual blood stages. Deletion of its P. berghei ortholog instead resulted in impaired sporozoite formation in the mosquito vector. While parasites lacking PbMCP2 were able to infect mosquito midguts and form oocysts, only few of them appeared to produce midgut sporozoites. Consequently, very few sporozoites colonized mosquito salivary glands. While lack of MCP2 does not seem to affect vertebrate-to-mosquito transmission as anticipated, it appears necessary for life cycle progression. Together, the findings presented here underline the importance of transporter proteins for Plasmodium parasites throughout their life cycle and contribute to our understanding of their roles in the different life cycle stages of malarial parasites.

The in vitro production of gametocytes and oocysts of the apicomplexan parasite genus Eimeria is still a challenge in coccidiosis research. Until today, an in vitro development of gametocytes or oocysts had only been shown in some Eimeria species. For several mammalian Eimeria species, partial developments could be achieved in different cell types, but a development up to gametocytes or oocysts is still lacking. This study compares several permanent cell lines with primary fetal cells of the black rat (Rattus norvegicus) concerning the qualitative in vitro development of the rat parasite Eimeria nieschulzi. With the help of transgenic parasites, the developmental progress was documented. The selected Eimeria nieschulzi strain constitutively expresses the yellow fluorescent protein and a macrogamont specific upregulated red tandem dimer tomato. In the majority of all investigated host cells the development stopped at the second merozoite stage. In a mixed culture of cells derived from inner fetal organs the development of schizont generations I-IV, macrogamonts, and oocysts were observed in crypt-like organoid structures. Microgamonts and microgametes could not be observed and oocysts did not sporulate under air supply. By immunohistology, we could confirm that wild-type E. nieschulzi stages can be found in the crypts of the small intestine. The results of this study may be helpful for characterization of native host cells and for development of an in vitro cultivation system for Eimeria species.

The in vitro production of gametocytes and oocysts of the apicomplexan parasite genus Eimeria is still a challenge in coccidiosis research. Until today, an in vitro development of gametocytes or oocysts had only been shown in some Eimeria species. For several mammalian Eimeria species, partial developments could be achieved in different cell types, but a development up to gametocytes or oocysts is still lacking. This study compares several permanent cell lines with primary fetal cells of the black rat (Rattus norvegicus) concerning the qualitative in vitro development of the rat parasite Eimeria nieschulzi. With the help of transgenic parasites, the developmental progress was documented. The selected Eimeria nieschulzi strain constitutively expresses the yellow fluorescent protein and a macrogamont specific upregulated red tandem dimer tomato. In the majority of all investigated host cells the development stopped at the second merozoite stage. In a mixed culture of cells derived from inner fetal organs the development of schizont generations I-IV, macrogamonts, and oocysts were observed in crypt-like organoid structures. Microgamonts and microgametes could not be observed and oocysts did not sporulate under air supply. By immunohistology, we could confirm that wild-type E. nieschulzi stages can be found in the crypts of the small intestine. The results of this study may be helpful for characterization of native host cells and for development of an in vitro cultivation system for Eimeria species.