TOXOPLASMA INVASION OF MAMMALIAN-CELLS IS POWERED BY THE ACTIN CYTOSKELETON OF THE PARASITE

Toxoplasma gondii is an obligate intracellular parasite that invades a wide range of vertebrate host cells. We demonstrate that invasion is critically dependent on actin filaments in the parasite, but not the h ost cell. Invasion into cytochalasin D (CD)-resistant host cells was b locked by CD, while parasite mutants invaded wild-type host cells in t he presence of drug. CD resistance in Toxoplasma was mediated by a poi nt mutation in the single-copy actin gene ACT1. Transfection of the mu tant act1 allele into wild-type Toxoplasma conferred motility and inva sion in the presence of CD. We conclude that host cell invasion by Tox oplasma, and likely by related Apicomplexans, is actively powered by a n actin-based contractile system in the parasite.