Quantitative analysis of Plasmodium ookinete motion in three dimensions suggests a critical role for cell shape in the biomechanics of malaria parasite gliding motility.
Bottom Line: Currently accepted models suggest it results from a specifically organized cellular motor that produces a rearward directional force.Using single-cell tracking and numerical analysis of parasite motion in 3D, our analysis demonstrates that ookinetes move with a conserved left-handed helical trajectory.Through comparisons of 3D movement between wild-type ookinetes and a cytoskeleton-knockout mutant we demonstrate that perturbation of cell shape changes motion from helical to broadly linear.
Affiliation: Victoria Research Laboratory, National ICT Australia (NICTA), Department of Computing and Information Systems, University of Melbourne, Melbourne, Vic., 3010, Australia.Show MeSH
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Mentions: To explore whether ookinete movement can be described in general terms, we extended the current in vitro Matrigel assay (Ishino et al., 2006; Moon et al., 2009; Volkmann et al., 2012) towards a more quantitative format that could measure ookinete motion in 3D space and use the parameters of this movement to build a model for idealized ookinete motility (see Experimental procedures). Reconstruction of tracks in 3D clearly confirmed the characteristic helical motion paths for ookinetes (Fig. 2A and B and Supplementary Movies S1–S3). Re‐centring motility tracks in each assay at a single point, demonstrated that motion is random in 3D space, showing no overall bias in directionality (Fig. 2C; Wilcoxon signed‐rank test for the differences between x, y or z co‐ordinates for each track at the beginning and end of movie P‐values 0.30, 0.72 and 0.09, respectively, n = 52; see Supplementary Discussion for extended discussion). While obviously lacking potential host chemotactic cues in our assay format, the random distribution is consistent with our imaging of the entire infected midgut excluding gravitational forces in the colonization process. Finally, although predominantly focused on an in vitro description of motility, we wanted to explore whether motion in a Matrigel assay is qualitatively similar to in vivo ookinete motility. Towards assessing this, 3D tracks were reconstructed from real‐time in vivo imaging of the same fluorescent ookinetes travelling through an explanted infected A. stephensi mosquito midgut. Because of difficulty in controlling the timing of ookinete development and mosquito infections, only a few events were captured that could facilitate detailed description (n = 4). However, of those captured, chiral motion was clearly apparent (Fig. 2D and E and Supplementary Movies S4 and S5) and, while speed was reduced (e.g. apparent speed ∼ 10.5 in vitro versus ∼ 7 μm min−1in vivo), the approximate coherence between our in vitro and in vivo imaging data is consistent with motion paths seen with previous in vitro and in vivo work (Freyvogel, 1966; Vlachou et al., 2004; Volkmann et al., 2012).
Affiliation: Victoria Research Laboratory, National ICT Australia (NICTA), Department of Computing and Information Systems, University of Melbourne, Melbourne, Vic., 3010, Australia.