Abstract
Increasing evidence shows that the spatial organization of transcription is an important epigenetic factor in eukaryotic gene regulation. The malaria parasite Plasmodium falciparum shows a remarkably complex pattern of gene expression during the erythrocytic cycle, paradoxically contrasting with the relatively low number of putative transcription factors encoded by its genome. The spatial organization of nuclear subcompartments has been correlated with the regulation of virulence genes. Here, we investigate the nuclear architecture of transcription during the asexual cycle of malaria parasites. As in mammals, transcription is organized into discrete nucleoplasmic sites in P. falciparum, but in a strikingly lower number of foci. An automated analysis of 3D images shows that the number and intensity of transcription sites vary significantly between rings and trophozoites, although the nuclear volume remains constant. Transcription sites are spatially reorganized during the asexual cycle, with a higher proportion of foci located in the outermost nuclear region in rings, whereas in trophozoites, foci are evenly distributed throughout the nucleoplasm. As in higher eukaryotes, transcription sites are predominantly found in areas of low chromatin density. Immunofluorescence analysis shows that transcription sites form an exclusive nuclear compartment, different from the compartments defined by the silenced or active chromatin markers. In conclusion, these data suggest that transcription is spatially contained in discrete foci that are developmentally regulated during the asexual cycle of malaria parasites and located in areas of low chromatin density.
Highlights
Almost half of the world population lives in areas of endemic malaria, a tropical disease that causes approximately 800,000 deaths every year
The Automated Analysis of 3D Images Indicated that Transcription Sites are Dynamic Structures Reorganized during the Asexual Cycle
Given our interest in studying the spatial organization of transcription in P. falciparum, we standardized the technique of incorporation of bromouridine 59-triphosphate (BrUTP) for this parasite
Summary
Almost half of the world population lives in areas of endemic malaria, a tropical disease that causes approximately 800,000 deaths every year. Plasmodium falciparum, the parasite that causes severe malaria, has a complex life cycle with several distinct stages of development, each characterized by unique morphological, physiological and molecular features. Despite progress in sequencing the genome of the parasite [1] and studies of the transcriptome [2,3], the molecular mechanisms of gene expression and regulation in malaria parasites remain poorly understood. The apparent absence of transcription factors in Plasmodium has been challenged by the identification of the first family of putative transcription factors specific to Apicomplexa, the ApiAP2 [1,6,7]
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