Die Rolle posttranslationaler Histon-Modifikationen zur Genregulierung während der Gametozyten-Entwicklung und Transmission des Malariaerregers Plasmodium falciparum
Malaria is still one of the deadliest diseases worldwide and is caused by parasites of the genus Plasmodium which exhibit a complex life cycle with fast asexual and sexual stage shifts. Therefore a precise gene expression to activate and deactivate the right repertoires of genes at the right time is needed. Among other control mechanisms this can be controlled by epigenetic modifications like histone acetylation and methylation. Epigenetic modifications so far have been mainly studied in asexual blood stages showing essential functions in virulence processes like host cell invasion and the induction of gametocyte formation. Treatment with inhibitors against histone modifying enzymes like histone methyltransferases (HMTs/PfSETs), histone acetyltransferases (HATs) and histone deacetylases (HDACs) already revealed an anti-malarial effect as well as deregulated gene expression. Due to emerging resistances this investigated effects reveal that these enzymes are extremely interesting as new prime targets to fight the infectious disease. The aim of this work was to investigate the posttranslational epigenetic modifications, like histone acetylation and methylation caused by HMTs/PfSETs and HDACs during the development of gametocytes as well as during human-to-mosquito transmission of the parasite. One goal of this study were chemical loss-of-function studies using the HDAC inhibitor TSA and the HMT inhibitor Bix-01294 which revealed a strong effect of these inhibitors on the development of the gametocytes and a slight effect on micro- and macrogametes as well as zygotes. The association of acetylated histones H3 and H4 and genes, which are upregulated after TSA-treatment, as shown via microarray analysis could be demonstrated by ChIP-qPCR analyses. Additionally, knockout mutants of PfSET2, PfSET8 and PfSET10 were generated by gene disruption for further functional and phenotypic characterization of these HMTs/PfSETs. Comparison of the PfSET10KO mutant and the wild-type strain of P. falciparum revealed neither morphological differences nor a difference in growth during the asexual intraerythrocytic phase, but a reduction of gametocytes and a delay in gametocyte maturation in the KO mutant. Further studies on the KO mutants would help to reveal the important role of these histone-modifying enzymes in the malaria parasite P. falciparum in more detail. The results of this work confirmed the important role of histone modifications during the sexual phase of the malaria parasite P. falciparum and laid the basis for further studies regarding the exact function. The data of this work and further characterization of the histone modifying enzymes HMTs/ PfSETs, HATs and HDACs could be used to develop malaria transmission-blocking interventions
