The DNA-binding protein PfAP2-G is found to be a master regulator of sexual development in the malaria parasite; this protein appears to regulate early gametocytogenesis and is epigenetically silenced in the majority of blood-stage parasites. For malaria parasites to be transmitted to the mosquito vector they must undergo sexual development and produce gametocytes. The molecular mechanisms underlying the commitment to gametocyte development have been unclear. Two complementary manuscripts now show that AP2-G, a member of the apicomplexan AP2 family of transcription factors, is a master regulator of sexual development in the malaria parasite, acting as a developmental switch by triggering the transcription of early gametocyte genes. Abhinav Sinha et al. worked with the rodent malaria parasite Plasmodium berghei, and Björn Kafsack et al. with the human pathogen P. falciparum. AP2-G activity in human infectious malaria parasites could be a potential target for antimalarials designed to interfere with gametocyte formation. The life cycles of many parasites involve transitions between disparate host species, requiring these parasites to go through multiple developmental stages adapted to each of these specialized niches. Transmission of malaria parasites (Plasmodium spp.) from humans to the mosquito vector requires differentiation from asexual stages replicating within red blood cells into non-dividing male and female gametocytes. Although gametocytes were first described in 1880, our understanding of the molecular mechanisms involved in commitment to gametocyte formation is extremely limited, and disrupting this critical developmental transition remains a long-standing goal1. Here we show that expression levels of the DNA-binding protein PfAP2-G correlate strongly with levels of gametocyte formation. Using independent forward and reverse genetics approaches, we demonstrate that PfAP2-G function is essential for parasite sexual differentiation. By combining genome-wide PfAP2-G cognate motif occurrence with global transcriptional changes resulting from PfAP2-G ablation, we identify early gametocyte genes as probable targets of PfAP2-G and show that their regulation by PfAP2-G is critical for their wild-type level expression. In the asexual blood-stage parasites pfap2-g appears to be among a set of epigenetically silenced loci2,3 prone to spontaneous activation4. Stochastic activation presents a simple mechanism for a low baseline of gametocyte production. Overall, these findings identify PfAP2-G as a master regulator of sexual-stage development in malaria parasites and mark the first discovery of a transcriptional switch controlling a differentiation decision in protozoan parasites.

Malaria parasites must produce gametocytes for transmission to the mosquito vector, although the molecular mechanisms underlying commitment to gametocyte production remain unclear; here this process is found to be controlled by PbAP2-G, a member of the ApiAP2 family of DNA-binding proteins, in the rodent-infecting Plasmodium berghei parasite. For malaria parasites to be transmitted to the mosquito vector they must undergo sexual development and produce gametocytes. The molecular mechanisms underlying the commitment to gametocyte development have been unclear. Two complementary manuscripts now show that AP2-G, a member of the apicomplexan AP2 family of transcription factors, is a master regulator of sexual development in the malaria parasite, acting as a developmental switch by triggering the transcription of early gametocyte genes. Abhinav Sinha et al. worked with the rodent malaria parasite Plasmodium berghei, and Björn Kafsack et al. with the human pathogen P. falciparum. AP2-G activity in human infectious malaria parasites could be a potential target for antimalarials designed to interfere with gametocyte formation. Commitment to and completion of sexual development are essential for malaria parasites (protists of the genus Plasmodium) to be transmitted through mosquitoes1. The molecular mechanism(s) responsible for commitment have been hitherto unknown. Here we show that PbAP2-G, a conserved member of the apicomplexan AP2 (ApiAP2) family of DNA-binding proteins, is essential for the commitment of asexually replicating forms to sexual development in Plasmodium berghei, a malaria parasite of rodents. PbAP2-G was identified from mutations in its encoding gene, PBANKA_143750, which account for the loss of sexual development frequently observed in parasites transmitted artificially by blood passage. Systematic gene deletion of conserved ApiAP2 genes in Plasmodium confirmed the role of PbAP2-G and revealed a second ApiAP2 member (PBANKA_103430, here termed PbAP2-G2) that significantly modulates but does not abolish gametocytogenesis, indicating that a cascade of ApiAP2 proteins are involved in commitment to the production and maturation of gametocytes. The data suggest a mechanism of commitment to gametocytogenesis in Plasmodium consistent with a positive feedback loop involving PbAP2-G that could be exploited to prevent the transmission of this pernicious parasite.

Perforin-like proteins are expressed by many bacterial and protozoan pathogens, yet little is known about their function or mode of action. Here, we describe Toxoplasma perforin-like protein 1 (TgPLP1), a secreted perforin-like protein of the intracellular protozoan pathogen Toxoplasma gondii that displays structural features necessary for pore formation. After intracellular growth, TgPLP1-deficient parasites failed to exit normally, resulting in entrapment within host cells. We show that this defect is due to an inability to rapidly permeabilize the parasitophorous vacuole membrane and host plasma membrane during exit. TgPLP1 ablation had little effect on growth in culture but resulted in a reduction greater than five orders of magnitude of acute virulence in mice. Perforin-like proteins from other intracellular pathogens may play a similar role in microbial egress and virulence.