Directional gene expression and antisense transcripts in sexual and asexual stages of Plasmodium falciparum

Abstract

BackgroundIt has been shown that nearly a quarter of the initial predicted gene models in the Plasmodium falciparum genome contain errors. Although there have been efforts to obtain complete cDNA sequences to correct the errors, the coverage of cDNA sequences on the predicted genes is still incomplete, and many gene models for those expressed in sexual or mosquito stages have not been validated. Antisense transcripts have widely been reported in P. falciparum; however, the extent and pattern of antisense transcripts in different developmental stages remain largely unknown.ResultsWe have sequenced seven bidirectional libraries from ring, early and late trophozoite, schizont, gametocyte II, gametocyte V, and ookinete, and four strand-specific libraries from late trophozoite, schizont, gametocyte II, and gametocyte V of the 3D7 parasites. Alignment of the cDNA sequences to the 3D7 reference genome revealed stage-specific antisense transcripts and novel intron-exon splicing junctions. Sequencing of strand-specific cDNA libraries suggested that more genes are expressed in one direction in gametocyte than in schizont. Alternatively spliced genes, antisense transcripts, and stage-specific expressed genes were also characterized.ConclusionsIt is necessary to continue to sequence cDNA from different developmental stages, particularly those of non-erythrocytic stages. The presence of antisense transcripts in some gametocyte and ookinete genes suggests that these antisense RNA may play an important role in gene expression regulation and parasite development. Future gene expression studies should make use of directional cDNA libraries. Antisense transcripts may partly explain the observed discrepancy between levels of mRNA and protein expression.

The RNA-binding protein PfPuf1 functions in the maintenance of gametocytes in Plasmodium falciparum

“…GFP signal was monitored with fluorescence microscopy throughout the entire duration of gametocyte development (Fig. 1E), but was not noticeable during asexual stages, which is in concordance with the lack of PfPuf1 transcript in asexual stages as revealed by microarray (Le Roch et al, 2003) and RNAseq (Lopez-Barragan et al, 2011) analyses. PfPuf1-GFP was localized in the cytoplasm of developing gametocytes, sometimes with a punctate appearance, especially at later stages.…”

A Plasmodium yoelii Mei2-Like RNA Binding Protein Is Essential for Completion of Liver Stage Schizogony

“…However, PlasMei2 is not required for blood stage schizogony, highlighting that liver stage schizogony is regulated by unique factors. Although the lack of PlasMei2 had no effect on asexual or sexual blood stage development in P. yoelii, evidence exists for PlasMei2 transcription in the mature P. falciparum gametocyte (35), suggesting that PlasMei2 may be required for P. falciparum gametocyte maturation, although this remains to be confirmed. The essentiality of PlasMei2 expression in the liver is likely necessitated by the far greater magnitude of liver stage parasite replication, compared to the blood stage, requiring an even more tightly regulated process to ensure proper endomitosis and the coordinated maturation of tens of thousands of exoerythrocytic merozoites.…”

Translational repression of the cpw-wpc gene family in the malaria parasite Plasmodium

“…4 wpc gene family in P. falciparum and P. berghei [8,9] and four P. yoelii cpw-wpc genes were detected in gametocytes and young ookinetes [10]. Twenty-two cpw-wpc genes from three species are thus upregulated in gametocytes, suggesting a conserved role for this gene family during sexual development and transmission of the human and two rodent malaria species.…”