A GFP-actin reporter line to explore microfilament dynamics across the malaria parasite lifecycle.

Malaria parasite motility relies on an internal parasite actomyosin motor that, when linked to the host cell substrate, propels motile zoites forward. Despite their key role in this process, attempts to visualize actin microfilaments (F-actin) during motility and under native microscopy conditions have not to date been successful. Towards facilitating their visualization we present here a Plasmodium berghei transgenic line in which a green fluorescent protein (GFP)-actin fusion is constitutively expressed through the lifecycle. Focused investigation of the largest motile form, the insect stage ookinete, demonstrates a large cytosolic pool of actin with no obvious F-actin structures. However, following treatment with the actin filament-stabilizing drug Jasplakinolide, we show evidence for concentration of F-actin dynamics in the parasite pellicle and at polar apices. These observations support current models for gliding motility and establish a cellular tool for further exploration of the diverse roles actin is thought to play throughout parasite development.