Conditional expression of apical membrane antigen 1 in Plasmodium falciparum shows it is required for erythrocyte invasion by merozoites.
Bottom Line: DiCre-mediated excision of the loxP-flanked Pfama1 gene results in approximately 80% decreased expression of the protein within one intraerythrocytic growth cycle.This reduces growth by 40%, due to decreased invasion efficiency characterized by a post-invasion defect in sealing of the parasitophorous vacuole.These results show that PfAMA1 is an essential protein for merozoite invasion in P. falciparum and either directly or indirectly plays a role in resealing of the red blood cell at the posterior end of the invasion event.
Affiliation: The Walter and Eliza Hall Institute of Medical Research, Melbourne, Vic., 3052, Australia.Show MeSH
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Mentions: Rapamycin-induced Pfama1 deletion resulted in a significant reduction of merozoite invasion and we used real time imaging to investigate the mechanistic defect. Live W2mef/AMA1-loxP/DiCre parasites were imaged under normal growth conditions following treatment with or without rapamycin. Late-stage schizonts were imaged by time-lapse microscopy for periods of 15–30 min. Following schizont rupture, untreated W2mef/AMA1-loxP parasites merozoites behaved similarly to wild type merozoites in that those that contacted erythrocytes deformed their target cells for several seconds before penetration (Fig. 6A) (Gilson and Crabb, 2009). Invasion itself lasted approximately 10 s after which the erythrocyte underwent echinocytosis 30–60 s later. Echinocytosis appears to be caused by dehydration of the host cell (Tiffert et al., 2005) and took an average of 376 s for recovery. During the recovery process the merozoite could be observed transforming into an amoeboid ring stage parasite (Gruring et al., 2011; Riglar et al., 2011). Of 38 attempted invasions observed for untreated merozoites 35 appeared successful and 3 failed (Fig. 6D). In one of the failed invasions the merozoite deformed the erythrocyte, triggered its echinocytosis but failed to penetrate and remained attached to the outside of the erythrocyte. In the other two failed invasions the merozoites penetrated, triggered echinocytosis but then reversed out of the invasion site back onto the outside of the erythrocyte.
Affiliation: The Walter and Eliza Hall Institute of Medical Research, Melbourne, Vic., 3052, Australia.