Global Release of Translational Repression Across Plasmodium's Host-to-Vector Transmission Event
Malaria parasites must be able to respond quickly to their environment, including during their transmission between mammalian hosts and mosquito vectors. Therefore, before transmission, female gametocytes proactively produce and translationally repress mRNAs that encode essential proteins that the zygote requires to establish a new infection. This essential regulatory control requires the orthologues of DDX6 (DOZI) and LSM14 (CITH), which along with ALBA proteins, form a translationally repressive complex in female gametocytes that associates with many of the affected mRNAs. However, while the release of translational repression of individual mRNAs has been documented, the details of the global release of translational repression have not. Moreover, the changes in spatial arrangement and composition of the DOZI/CITH/ALBA complex that contribute to translational control are also not known. Therefore, we have conducted the first comparative transcriptomics and proteomics of Plasmodium parasites across the host-to-vector transmission event to document the global release of translational repression. Using female gametocytes and zygotes of P. yoelii, we find that over 200 transcripts are released for translation soon after fertilization, including those with essential functions for the zygote. However, we also observed that some transcripts remain repressed beyond this point. In addition, we have used TurboID-based proximity proteomics to interrogate the spatial and compositional changes in the DOZI/CITH/ALBA complex across this transmission event. Consistent with recent models of translational control, proteins that associate with either the 5' or 3' end of mRNAs are in close proximity to one another during translational repression in female gametocytes and then dissociate upon release of repression in zygotes. These protein interactions in female gametocytes were further validated through structured illumination microscopy and ultrastructure expansion microscopy. Together, these data provide a model for the essential translational control mechanisms used by malaria parasites to promote their efficient transmission. Overall design: Female gametocytes and zygotes were purified by flow cytometry, RNA was purified by a Qiagen Rneasy kit with in-solution DNaseI digestion, and used for library preparation using the Illumina stranded mRNA kit for 150nt single end reads.