Identification of genes required for Plasmodium gametocyte-to-sporozoite development in the mosquito vector

Elevated NAD+ drives Sir2A-mediated GCβ deacetylation and OES localization for Plasmodium ookinete gliding and mosquito infection

cGMP signal-activated ookinete gliding is essential for mosquito midgut infection of Plasmodium in malaria transmission. During ookinete development, cGMP synthesizer GCβ polarizes to a unique localization "ookinete extrados site" (OES) until ookinete maturation and activates cGMP signaling for initiating parasite motility. However, the mechanism underlying GCβ translocation from cytosol to OES remains elusive. Here, we use protein proximity labeling to search the GCβ-interacting proteins in ookinetes of the rodent malaria parasite P. yoelii, and find the top hit Sir2A, a NAD+-dependent sirtuin family deacetylase. Sir2A interacts with GCβ throughout ookinete development. In mature ookinetes, Sir2A co-localizes with GCβ at OES in a mutually dependent manner. Parasites lacking Sir2A lose GCβ localization at OES, ookinete gliding, and mosquito infection, phenocopying GCβ deficiency. GCβ is acetylated at gametocytes but is deacetylated by Sir2A for OES localization at mature ookinetes. We further demonstrate that the level of NAD+, an essential co-substrate for sirtuin, increases during the ookinete development. NAD+ at its maximal level in mature ookinetes promotes Sir2A-catalyzed GCβ deacetylation, ensuring GCβ localization at OES. This study highlights the spatiotemporal coordination of cytosolic NAD+ level and NAD+-dependent Sir2A in regulating GCβ deacetylation and dynamic localization for Plasmodium ookinete gliding.

Ready for renascence in mosquito: The regulation of gene expression in Plasmodium sexual development

Malaria remains one of the most perilous vector-borne infectious diseases for humans globally. Sexual gametocyte represents the exclusive stage at which malaria parasites are transmitted from the vertebrate to the Anopheles host. The feasible and effective approach to prevent malaria transmission is by addressing the sexual developmental processes, that is, gametocytogenesis and gametogenesis. Thus, this review will comprehensively cover advances in the regulation of gene expression surrounding the transmissible stages, including epigenetic, transcriptional, and post-transcriptional control.

The molecular mechanisms driving Plasmodium cell division

Malaria, a vector borne disease, is a major global health and socioeconomic problem caused by the apicomplexan protozoan parasite Plasmodium. The parasite alternates between mosquito vector and vertebrate host, with meiosis in the mosquito and proliferative mitotic cell division in both hosts. In the canonical eukaryotic model, cell division is either by open or closed mitosis and karyokinesis is followed by cytokinesis; whereas in Plasmodium closed mitosis is not directly accompanied by concomitant cell division. Key molecular players and regulatory mechanisms of this process have been identified, but the pivotal role of certain protein complexes and the post-translational modifications that modulate their actions are still to be deciphered. Here, we discuss recent evidence for the function of known proteins in Plasmodium cell division and processes that are potential novel targets for therapeutic intervention. We also identify key questions to open new and exciting research to understand divergent Plasmodium cell division.

Revisiting the determinants of malaria transmission

Malaria parasites have coevolved with humans over thousands of years, mirroring their migration out of Africa. They persist to this day, despite continuous elimination efforts worldwide. These parasites can adapt to changing environments during infection of human and mosquito, and when expanding the geographical range by switching vector species. Recent studies in the human malaria parasite, Plasmodium falciparum, identified determinants governing the plasticity of sexual conversion rates, sex ratio, and vector competence. Here we summarize the latest literature revealing environmental, epigenetic, and genetic determinants of malaria transmission.

The Multiple Roles of LCCL Domain-Containing Proteins for Malaria Parasite Transmission

Multi-protein complexes are crucial for various essential biological processes of the malaria parasite Plasmodium, such as protein synthesis, host cell invasion and adhesion. Especially during the sexual phase of the parasite, which takes place in the midgut of the mosquito vector, protein complexes are required for fertilization, sporulation and ultimately for the successful transmission of the parasite. Among the most noticeable protein complexes of the transmission stages are the ones formed by the LCCL domain-containing protein family that play critical roles in the generation of infective sporozoites. The six members of this protein family are characterized by numerous adhesive modules and domains typically found in secreted proteins. This review summarizes the findings of expression and functional studies on the LCCL domain-containing proteins of the human pathogenic P. falciparum and the rodent-infecting P. berghei and discusses the common features and differences of the homologous proteins.

Intracellular Plasmodium aquaporin 2 is important for sporozoite production in the mosquito vector and malaria transmission

Malaria remains a devastating disease and, with current measures failing to control its transmission, there is a need for novel interventions. A family of proteins that have long been pursued as potential intervention targets are aquaporins, which are channels facilitating the movement of water and other solutes across membranes. We identify an aquaporin in malaria parasites and demonstrate that it is important for completion of Plasmodium development in the mosquito vector. Disruption of AQP2 in the human parasite Plasmodium falciparum and the rodent parasite Plasmodium berghei blocks sporozoite production inside oocysts established on mosquito midguts, greatly limiting parasite infection of salivary glands and transmission to a new host. In vivo epitope tagging of AQP2 in P. berghei, combined with immunofluorescence assays, reveals that the protein is localized in vesicle-like organelles found in the cytoplasm of gametocytes, ookinetes, and sporozoites. The number of these organelles varies between individual parasites and lifecycle stages suggesting that they are likely part of a dynamic endomembrane system. Phylogenetic analysis confirms that AQP2 is unique to malaria and closely related parasites and most closely resembles intracellular aquaporins. Structure prediction analyses identify several unusual features, including a large accessory extracellular loop and an arginine-to-phenylalanine substitution in the selectivity filter principally determining pore function, a unique feature among known aquaporins. This in conjunction with the importance of AQP2 for malaria transmission suggests that AQP2 may be a fruitful target of antimalarial interventions.

Sex determination and transmission: Leveraging genetic screens to reveal Plasmodium's secrets

Genes and regulatory mechanisms governing malaria parasite transmission and development in mosquitoes are incompletely understood. Recently, Russell and colleagues identified genes required for parasite sexual development. In this issue of Cell Host & Microbe, Ukegbu and colleagues report a genetic approach to study genes enabling parasite survival in mosquito stages.