Revealing the Sequence and Resulting Cellular Morphology of Receptor-Ligand Interactions during Plasmodium falciparum Invasion of Erythrocytes
Fig 5
Immediately prior to invasion a Fluo-4 signal appears at the junction of the merozoite and host cell suggesting an opening between the erythrocyte cytoplasm and the merozoite.
(A) Selected images from videos of purified W2mef schizonts added to Fluo-4 AM-labelled erythrocytes with (right) or without (left) cytD treatment. Outlines of the merozoite boundaries are transposed onto the Fluo-4 images to give an indication of where the Fluo-4 signal is relative to the merozoite. For those without cytD treatment, in the left panel, the direction of invasion is shown with an arrow, or a circle with a dot if the invasion is going into the plane of the image. (B) A timeline to scale showing the average length of time for each stage of the invasion process for untreated W2mef schizonts invading Fluo-4-treated erythrocytes. Above the timeline the average length of the Fluo-4 signal is indicated by the bar, with minimum and maximum shown by the whiskers, and placed on the timeline relative to the start of invasion. (C) Mean and SD for each stage of invasion and the timing of the punctate calcium signals observed for untreated W2mef schizonts invading Fluo-4-treated erythrocytes. (D) Model showing reorientation and illustrating how an open junction between merozoite rhoptries containing Ca2+ and erythrocyte cytoplasm containing Fluo-4 could mix at the merozoite apex, indicating a permeabilization or opening of the erythrocyte membrane. (E) Percent of total merozoites with punctate calcium signals which cause echinocytosis or do not, and within these the proportion which invade.