LAUSR

Significance A better understanding of the molecular mechanisms underlying the development of Plasmodium parasites in Anopheles mosquitoes would facilitate the development of malaria vaccines and of novel strategies to interrupt disease transmission. We characterized, at the single-cell level, the gene expression profiles of sporozoites from the rodent malaria parasite Plasmodium berghei, throughout their development in mosquitoes and upon salivation. Our analyses reveal heterogeneity in gene expression among parasites isolated from the same anatomical location, suggesting that parasite development is asynchronous in mosquitoes. In addition, our results highlight the role of gene expression changes in regulating the ability of sporozoites to remain quiescent in the salivary glands, and their rapid reactivation upon salivation. Despite the critical role of Plasmodium sporozoites in malaria transmission, we still know little about the mechanisms underlying their development in mosquitoes. Here, we use single-cell RNA sequencing to characterize the gene expression profiles of 16,038 Plasmodium berghei sporozoites isolated throughout their development from midgut oocysts to salivary glands, and from forced salivation experiments. Our results reveal a succession of tightly regulated changes in gene expression occurring during the maturation of sporozoites and highlight candidate genes that could play important roles in oocyst egress, sporozoite motility, and the mechanisms underlying the invasion of mosquito salivary glands and mammalian hepatocytes. In addition, the single-cell data reveal extensive transcriptional heterogeneity among parasites isolated from the same anatomical site, suggesting that Plasmodium development in mosquitoes is asynchronous and regulated by intrinsic as well as environmental factors. Finally, our analyses show a decrease in transcriptional activity preceding the translational repression observed in mature sporozoites and associated with their quiescent state in salivary glands, followed by a rapid reactivation of the transcriptional machinery immediately upon salivation.