The single cell transcriptional signature of sexual commitment in the human malaria parasite Plasmodium falciparum

Abstract

<ns5:p> Background Malaria remains a global health challenge, with most fatal cases caused by <ns5:italic>Plasmodium falciparum</ns5:italic> in sub-Saharan Africa. A critical bottleneck in the <ns5:italic>Plasmodium</ns5:italic> life cycle is the transmission from human to mosquito, which requires a subset of blood stage parasites to switch from asexual to sexual replication in a process known as stage conversion. In <ns5:italic>P. falciparum</ns5:italic> , stage conversion is known to be environmentally sensitive, notably to limiting levels of the immunomodulatory lipid lysophosphatidylcholine (LysoPC). Methods Here, we use single cell RNA sequencing (scRNAseq) to deconvolve the transcriptional signature of parasites upon limiting LysoPC levels under controlled <ns5:italic>in vitro</ns5:italic> conditions. Results Our data validate previous findings from bulk RNA sequencing, demonstrating a general compensatory metabolic response and reduced nutrient transport triggered by reduced LysoPC levels. Further, we define an initial transcriptional signature of sexual commitment, consisting of 22 genes conserved across two genetically diverse parasite strains. This signature includes an entire genetic locus encoding three proteins putatively involved in host-parasite interactions. Interestingly, the proportion of parasites expressing the transcriptional signature of sexual commitment was about twofold higher than the sexual conversion rate experimentally measured in the subsequent gametocyte cycle. Conclusions Together with recent data demonstrating that sexual commitment and conversion rates as measured by fluorescent reporter lines match closely, these data suggest that sexually committed schizonts may be in a transcriptionally bipotential state and sexual development becomes irreversible only at the post transcriptional level. Our study provides a rationale for systematic functional dissection of this elusive yet essential phase in the parasite cycle. </ns5:p>