A cascade of transcriptional repression determines sexual commitment and development in Plasmodium falciparum

Abstract

Gametocytogenesis, the process by which malaria parasites produce sexual forms that can infect mosquitoes, is essential for the transmission of malaria. A transcriptional switch of the pfap2-g gene triggers sexual commitment, but how the complex multi-step process is precisely programed remains largely unknown. Here, by systematic functional screening of a panel of ApiAP2 transcription factors, we identify six new ApiAP2 members associated with gametocytogenesis in Plasmodium falciparum. Among these, PfAP2-G5 (PF3D7_1139300) was found to be indispensable for gametocytogenesis. This factor suppresses the transcriptional activity of the pfap2-g gene via binding to both the upstream region and exonic gene body, the latter is linked to the maintenance of local heterochromatin structure, thereby preventing initiation of sexual commitment. Removal of this repressive effect through pfap2-g5 knockout disrupts the asexual replication cycle and promotes sexual commitment accompanied by upregulation of pfap2-g expression. However, the gametocytes produced fail to mature fully. Further analyses show that PfAP2-G5 is essential for gametocyte maturation, and causes the down-regulation of pfap2-g and a set of early gametocyte genes activated by PfAP2-G prior to gametocyte development. Collectively, our findings reveal a regulation cascade of gametocyte production in malaria parasites, and provide a new target for transmission blocking interventions.

Identification of Antimalarial Compounds that Inhibit Apicomplexan AP2 Proteins

“…Elucidation of the role of essential P. falciparum ApiAP2 proteins in the IDC is challenging due to the inability to knockout asexual blood stage essential genes from the parasite's haploid genome. Previous attempts to knockout AP2-EXP [27][28][29]33 failed to produce parasite lines in which the AP2 domain coding sequence was disrupted. We similarly did not recover transgenic parasites after attempting to completely disrupt the coding sequence for AP2-EXP using the targeted gene disruption (pSLI-TGD) system 51 in three independent attempts, suggesting that AP2-EXP is essential for the IDC (not shown).…”

“…Their plant-like origin distinguishes them from all other known transcription factors in humans or mosquitoes 20 . Over half of the ApiAP2 proteins are predicted to be essential for the IDC in P. falciparum based on a random mutagenesis screen 26 , and in targeted knockout screens only 11/23 ApiAP2 coding sequence disruptions attempted were successful [27][28][29] . In the rodent malaria model species P. berghei 30 and P. yoelii 31 , 11 ApiAP2 proteins have developmental lethal phenotypes in the sexual blood or mosquito stages.…”

“…In the rodent malaria model species P. berghei 30 and P. yoelii 31 , 11 ApiAP2 proteins have developmental lethal phenotypes in the sexual blood or mosquito stages. ApiAP2 transcription factors can cause activation or repression of transcription of specific genes, and they are involved in diverse lifecycle processes including invasion, mutually exclusive antigenic gene expression, sexual differentiation, and heat stress tolerance 27,[32][33][34][35][36][37][38][39][40] . Chromatin interacting proteins such as histone deacetylases and methyltransferases have received recent attention as potential drug targets against malaria parasites 41,42 .…”

The Plasmodium falciparum CCCH zinc finger protein ZNF4 plays an important role in gametocyte exflagellation through the regulation of male gametocyte enriched transcripts

“…The expression of AP2-G promotes the transcription of early gametocyte genes, which leads to gametocyte commitment and formation [4][5][6]. In a recent study, it was shown that another transcription factor AP2-G5 is essential for gametocyte maturation through the down-regulation of AP2-G and a set of genes activated by AP2-G prior to gametocyte development [7]. Other transcription factors such as AP2-FG and AP2-O3 have been shown to regulate gene expression in female gametocytes [8,9] and ookinete development by AP2-O family [10,11].…”

PfAP2-EXP2, an Essential Transcription Factor for the Intraerythrocytic Development of Plasmodium falciparum

“…According to latest research, scientists have successfully knocked out 11 ApiAP2 transcription factors in P. falciparum and have gained a preliminary insight into their functions ( Shang et al, 2021 ; Singh et al, 2021 ). PfAP2-G is recognized as the master positive regulator of sexual conversion between gametocyte commitment and development, while PfAP2-G5 and PfAP2-G2 work together as transcriptional repressors ( Kafsack et al, 2014 ; Sinha et al, 2014 ; Poran et al, 2017 ; Xu et al, 2020 ; Shang et al, 2021 ; Singh et al, 2021 ). Another ApiAP2 family member, which is named PfAP2-I, has been reported to regulate the process of invasion ( Santos et al, 2017 ).…”