The multiple functions of actin in apicomplexan parasites

The cytoskeletal protein actin is highly abundant and conserved in eukaryotic cells. It occurs in two different states‐ the globular (G‐actin) form, which can polymerise into the filamentous (F‐actin) form, fulfilling various critical functions including cytokinesis, cargo trafficking and cellular motility. In higher eukaryotes, there are several actin isoforms with nearly identical amino acid sequences. Despite the high level of amino acid identity, they display regulated expression patterns and unique non‐redundant roles. The number of actin isoforms together with conserved sequences may reflect the selective pressure exerted by scores of actin binding proteins (ABPs) in higher eukaryotes. In contrast, in many protozoans such as apicomplexan parasites which possess only a few ABPs, the regulatory control of actin and its multiple functions are still obscure. Here, we provide a summary of the regulation and biological functions of actin in higher eukaryotes and compare it with the current knowledge in apicomplexans. We discuss future experiments that will help us understand the multiple, critical roles of this fascinating system in apicomplexans. A filamentous actin (F‐actin) network connects individual daughter cells within the parasitophorous vacuole in Toxoplasma and Plasmodium parasites. Formin localization controls the direction of actin flow, which regulates transport and recycling of vesicles, and apicoplast inheritance. Vesicular transport is associated to both microtubules and F‐actin, which are in crosstalk with each other. Furthermore, scission and distribution of apicoplasts into daughter cells is dependent on DrpA and Myosin‐F. Additionally, in Plasmodium, actin dynamics may control uptake of haemoglobin/fusion of vesicles with the food vacuole, and the completion of cytokinesis.