Molecular characterization of mitochondria in asexual and sexual blood stages of Plasmodium falciparum.

Molecular mechanisms that regulate gene expression during development of asexual stage to sexual stage of Plasmodium falciparum in the human erythrocyte are largely unknown. There were apparent variations in ultrastructural characteristics of the mitochondrion between the two developing stages. The asexual stage's mitochondrion had developed less than that of the sexual stage. The respiratory complexes of the mitochondrial electron transport system in the asexual stage were approximately 8-10 times less active than those in the sexual stage. Using quantitative polymerase chain reaction to amplify the cytochrome b gene encoding a subunit of mitochondrial cytochrome c reductase, the amount of the cytochrome b gene of the sexual stage was calculated to be approximately 3 times higher than that obtained from the asexual stage. Moreover, using quantitative reverse-transcription polymerase chain reaction, a relatively high level of approximately 1.3-kb transcript mRNA of the cytochrome b gene was observed in the sexual stage compared to the asexual stage. A known single-copy chromosomal dihydrofolate reductase gene was found to have a similar amount in the two stages. These results suggest that the copy number of the mitochondrial gene, including transcriptional and translational mechanisms, plays a major regulatory role in differential expression during the development of the asexual to sexual stage of P. falciparum in the human cell.