Hence, the time the ookinete needs to develop is fixed and thus independent from species (reviewed in Dyer and Day, 2000 Talman et al., 2004 Kooij and Matuschewski, 2007 Pradel, 2007 Bennink et al., 2016 Josling et al., 2018). The exit of the ookinete from the mosquito midgut has to occur before the peritrophic membrane that protects the midgut epithelium from invaders has fully matured. The resulting zygote then develops to a motile ookinete during a period of 1 day. Sexual reproduction is initiated in the mosquito midgut, triggered by environmental factors (Fig. Following a period of maturation, which lasts between 2 and 10 days and again is species-dependent, mature gametocytes are able to transform into fertile gametes within less than 10 min, once taken up by a blood-feeding mosquito. The sexual phase begins with the formation of sexual precursor cells, the gametocytes, in the human red blood cells in response to host factors (Fig. Other processes of stage conversion are related to sexual reproduction.

ECM, extracellular matrix PL, phospholipid XA, xanthurenic acid. Stages during life cycle progression particularly dependent on extracellular signals are indicated (grey text box). The various asexual replication phases and the sexual reproduction phase are indicated (blue text box). falciparum in the human host and mosquito vector. The oocyst-specific replication phase requires between 7 and 30 days and in addition to the species dependency is influenced by the outside temperature (reviewed in Antinori et al., 2012). Another, slower progressing phase of replication occurs in the oocysts, which are attached to the midgut epithelium of the mosquito. Fast successive stage conversions occur during the intrahepatocytic replication phase in the human liver, which takes place over a period of 6–16 days, and the following recurrent intraerythrocytic replication cycles that each last between 1 and 3 days both replication phases are dependent on the Plasmodium species. These parasites pass through a life cycle that switches between a human and a mosquito host and includes various phases of stage conversions (Fig. Currently, five human pathogenic malaria parasites are known. Rapid responses to environmental changes are particularly important for the protozoan malaria parasite Plasmodium. In contrast to transcriptional control, the regulation of protein synthesis by post-transcriptional and translational mechanisms enables the cell to rapidly adjust to the environmental changes and protein synthesis can be activated or stopped within minutes after perception of the signal (reviewed in López-Maury et al., 2008). In general, the regulation of gene expression can occur on three levels, the transcriptional, the post-transcriptional and the translational level. Gene expression in a cell is up or downregulated in response to environmental triggers, such as changes in temperature, pH or nutrient availability. We here highlight recent findings on translational control during life cycle progression of Plasmodium and discuss the molecules involved in regulating protein synthesis. The main molecules controlling translation are highly conserved in malaria parasites and an increasing number of studies shed light on the interwoven pathways leading to the up or downregulation of protein synthesis in the diverse plasmodial stages. Three control mechanisms are currently proposed in Plasmodium, (1) global regulation that acts on the translation initiation complex (2) mRNA-specific regulation, involving cis control elements, mRNA-binding proteins and translational repressors and (3) induced mRNA decay by the Ccr4-Not and the RNA exosome complex. In particular, the quiescent transmission stages rely on translational control to rapidly adapt to the new environment, once they switch over from the human to the mosquito and vice versa. The regulation of translation is of special importance for malaria parasites, which pass through a complex life cycle that includes various replication phases in the different organs of the human and mosquito hosts and a sexual reproduction phase in the mosquito midgut. Translational control regulates the levels of protein synthesized from its transcript and is key for the rapid adjustment of gene expression in response to environmental stimuli.

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