High-mobility-group box nuclear factors of Plasmodium falciparum.

In eukaryotes, the high-mobility-group (HMG) nuclear factors are highly conserved throughout evolution and are divided into three families, including HGMB, characterized by an HMG box domain. Some HMGB factors are DNA structure specific and preferentially interact with distorted DNA sequences, trigger DNA bending, and hence facilitate the binding of nucleoprotein complexes that in turn activate or repress transcription. In Plasmodium falciparum, two HMGB factors were predicted: PfHMGB1 and PfHMGB2. They are small proteins, under 100 amino acids long, encompassing a characteristic HMG box domain closely related to box B of metazoan factors, which comprises two HMG box domains, A and B, in tandem. Computational analyses supported the conclusion that the Plasmodium proteins were genuine architectural HMGB factors, and in vitro analyses performed with both recombinant proteins established that they were able to interact with distorted DNA structures and bend linear DNA with different affinities. These proteins were detected in both asexual- and gametocyte-stage cells in Western blotting experiments and mainly in the parasite nuclei. PfHMGB1 is preferentially expressed in asexual erythrocytic stages and PfHMGB2 in gametocytes, in good correlation with transcript levels of expression. Finally, immunofluorescence studies revealed differential subcellular localizations: both factors were observed in the nucleus of asexual- and sexual-stage cells, and PfHMGB2 was also detected in the cytoplasm of gametocytes. In conclusion, in light of differences in their levels of expression, subcellular localizations, and capacities for binding and bending DNA, these factors are likely to play nonredundant roles in transcriptional regulation of Plasmodium development in erythrocytes.

PfMyb1, a Plasmodium falciparum transcription factor, is required for intra-erythrocytic growth and controls key genes for cell cycle regulation.

During the complex life cycle of Plasmodium falciparum, divided between mosquito and human hosts, the regulation of morphologic changes implies a fine control of transcriptional regulation. Transcriptional control, however, and in particular its molecular actors, transcription factors and regulatory motifs, are as yet poorly described in Plasmodium. In order to decipher the molecular mechanisms implicated in transcriptional regulation, a transcription factor belonging to the tryptophan cluster family was studied. In a previous work, the PfMyb1 protein, contained in nuclear extracts, was shown to have DNA binding activity and to interact specifically with myb regulatory elements. We used long pfmyb1 double-stranded RNA (dsRNA) to interfere with the cognate messenger expression. Parasite cultures treated with pfmyb1 dsRNA exhibited a 40% growth inhibition when compared with either untreated cultures or cultures treated with unrelated dsRNA, and parasite mortality occurred during trophozoite to schizont transition. In addition, the pfmyb1 transcript and protein decreased by as much as 80% in treated trophozoite cultures at the time of their maximum expression. The global effect of this partial loss of transcript and protein was investigated using a thematic DNA microarray encompassing genes involved in signal transduction, cell cycle and transcriptional regulation. SAM software enabled us to identify several genes that were differentially expressed and probably directly or indirectly under the control of PfMyb1. Using chromatin immuno-precipitation, we demonstrated that PfMyb1 binds, within the parasite nuclei, to several promoters and therefore participates directly in the transcriptional regulation of the corresponding genes. This study provides the first evidence of a regulation network involving a Plasmodium transcription factor.

Transcriptome of 3D7 and its gametocyte-less derivative F12 Plasmodium falciparum clones during erythrocytic development using a gene-specific microarray assigned to gene regulation, cell cycle and transcription factors.

During the complex life cycle of Plasmodium falciparum, through mosquito and human, the erythrocytic cycle is responsible for malarial disease and transmission. The regulation of events that occur during parasite development, such as proliferation and differentiation, implies a fine control of transcriptional activities that in turn governs the expression profiles of sets of genes. Pathways that underline gametocyte commitment are yet poorly understood even though kinases and transcription factors have been assumed to play a crucial role in this event. In order to understand the molecular mechanisms controlling the variation of gene expression profiles that might participate in early gametocytogenesis, the transcriptome of two clones, 3D7 and its gametocyte-less derivative F12, was compared at five time points of the erythrocytic asexual development. We have used a thematic DNA microarray containing 150 PCR fragments, representative of P. falciparum genes involved in signal transduction, cell cycle and transcriptional regulation. We identified several genes eliciting different expression profiles among which some implicated in gene regulation or encoding putative transcription factors. The differential expression of transcription factor and kinase transcripts observed in the two clones may enlighten genes that might have a role in impairment of the early gametocytogenesis of the F12 clone.