Toxoplasma Invasion Revisited

Cell Biology Apicomplexan parasites actively invade their host cell. Invasion depends on an arsenal of secreted invasion factors and the ability of the parasite to glide. The Myosin A (MyoA) motor complex, also known as the glideosome, is a multisubunit complex localized beneath the plasma membrane of the parasite. It is thought to provide the necessary force to move the parasite forward and is essential for gliding motility in Toxoplasma gondii and Plasmodium . Gliding mutants, however, retain the ability to invade host cells, albeit at reduced efficiency. To establish whether background expression of the respective protein in the knockdown mutants might be sufficient to drive host cell invasion, Andenmatten et al. generated a conditional recombination system based on dimerizable Cre recombinase, which they used to generate complete knockouts of three proteins—MyoA, the micronemal protein MIC2, and actin—each thought to be essential for host cell invasion in T. gondii. Surprisingly, each of the complete knockout mutants could invade host cells, and the MyoA and MIC2 knockouts could be maintained and grown in vitro, suggesting that alternative invasion strategies exist. As expected, parasites lacking MyoA were not able to move by gliding motility and consequently were significantly impaired in host cell egress. Nat. Meth. 10.1038/nmeth.2301 (2012).